Add js.Batch

Fixes #12626
Closes #7499
Closes #9978
Closes #12879
Closes #13113
Fixes #13116

61 files changed, 4495 insertions, 978 deletions

diff --git a/commands/hugobuilder.go b/commands/hugobuilder.go
index 51493938d..dcc5c099b 100644
--- a/commands/hugobuilder.go
+++ b/commands/hugobuilder.go
@@ -920,7 +920,11 @@ func (c *hugoBuilder) handleEvents(watcher *watcher.Batcher,
 
 			changed := c.changeDetector.changed()
 			if c.changeDetector != nil {
-				lrl.Logf("build changed %d files", len(changed))
+				if len(changed) >= 10 {
+					lrl.Logf("build changed %d files", len(changed))
+				} else {
+					lrl.Logf("build changed %d files: %q", len(changed), changed)
+				}
 				if len(changed) == 0 {
 					// Nothing has changed.
 					return
diff --git a/commands/server.go b/commands/server.go
index c2fee68b2..c4a8ddd29 100644
--- a/commands/server.go
+++ b/commands/server.go
@@ -32,6 +32,7 @@ import (
 	"path"
 	"path/filepath"
 	"regexp"
+	"sort"
 	"strconv"
 	"strings"
 	"sync"
@@ -210,16 +211,17 @@ func (f *fileChangeDetector) changed() []string {
 		}
 	}
 
-	return f.filterIrrelevant(c)
+	return f.filterIrrelevantAndSort(c)
 }
 
-func (f *fileChangeDetector) filterIrrelevant(in []string) []string {
+func (f *fileChangeDetector) filterIrrelevantAndSort(in []string) []string {
 	var filtered []string
 	for _, v := range in {
 		if !f.irrelevantRe.MatchString(v) {
 			filtered = append(filtered, v)
 		}
 	}
+	sort.Strings(filtered)
 	return filtered
 }
 
diff --git a/common/herrors/errors.go b/common/herrors/errors.go
index 40833e55c..c7ee90dd0 100644
--- a/common/herrors/errors.go
+++ b/common/herrors/errors.go
@@ -133,6 +133,21 @@ func IsNotExist(err error) bool {
 	return false
 }
 
+// IsExist returns true if the error is a file exists error.
+// Unlike os.IsExist, this also considers wrapped errors.
+func IsExist(err error) bool {
+	if os.IsExist(err) {
+		return true
+	}
+
+	// os.IsExist does not consider wrapped errors.
+	if os.IsExist(errors.Unwrap(err)) {
+		return true
+	}
+
+	return false
+}
+
 var nilPointerErrRe = regexp.MustCompile(`at <(.*)>: error calling (.*?): runtime error: invalid memory address or nil pointer dereference`)
 
 const deferredPrefix = "__hdeferred/"
diff --git a/common/herrors/file_error.go b/common/herrors/file_error.go
index 007a06b48..c8a48823e 100644
--- a/common/herrors/file_error.go
+++ b/common/herrors/file_error.go
@@ -384,7 +384,7 @@ func extractPosition(e error) (pos text.Position) {
 	case godartsass.SassError:
 		span := v.Span
 		start := span.Start
-		filename, _ := paths.UrlToFilename(span.Url)
+		filename, _ := paths.UrlStringToFilename(span.Url)
 		pos.Filename = filename
 		pos.Offset = start.Offset
 		pos.ColumnNumber = start.Column
diff --git a/common/hreflect/helpers.go b/common/hreflect/helpers.go
index 5113a3886..fc83165c7 100644
--- a/common/hreflect/helpers.go
+++ b/common/hreflect/helpers.go
@@ -223,6 +223,27 @@ func AsTime(v reflect.Value, loc *time.Location) (time.Time, bool) {
 	return time.Time{}, false
 }
 
+// ToSliceAny converts the given value to a slice of any if possible.
+func ToSliceAny(v any) ([]any, bool) {
+	if v == nil {
+		return nil, false
+	}
+	switch vv := v.(type) {
+	case []any:
+		return vv, true
+	default:
+		vvv := reflect.ValueOf(v)
+		if vvv.Kind() == reflect.Slice {
+			out := make([]any, vvv.Len())
+			for i := 0; i < vvv.Len(); i++ {
+				out[i] = vvv.Index(i).Interface()
+			}
+			return out, true
+		}
+	}
+	return nil, false
+}
+
 func CallMethodByName(cxt context.Context, name string, v reflect.Value) []reflect.Value {
 	fn := v.MethodByName(name)
 	var args []reflect.Value
diff --git a/common/hreflect/helpers_test.go b/common/hreflect/helpers_test.go
index 27b774337..119722261 100644
--- a/common/hreflect/helpers_test.go
+++ b/common/hreflect/helpers_test.go
@@ -50,6 +50,19 @@ func TestIsContextType(t *testing.T) {
 	c.Assert(IsContextType(reflect.TypeOf(valueCtx)), qt.IsTrue)
 }
 
+func TestToSliceAny(t *testing.T) {
+	c := qt.New(t)
+
+	checkOK := func(in any, expected []any) {
+		out, ok := ToSliceAny(in)
+		c.Assert(ok, qt.Equals, true)
+		c.Assert(out, qt.DeepEquals, expected)
+	}
+
+	checkOK([]any{1, 2, 3}, []any{1, 2, 3})
+	checkOK([]int{1, 2, 3}, []any{1, 2, 3})
+}
+
 func BenchmarkIsContextType(b *testing.B) {
 	type k string
 	b.Run("value", func(b *testing.B) {
diff --git a/common/maps/cache.go b/common/maps/cache.go
index cdc31a684..72c07e7ca 100644
--- a/common/maps/cache.go
+++ b/common/maps/cache.go
@@ -113,11 +113,14 @@ func (c *Cache[K, T]) set(key K, value T) {
 }
 
 // ForEeach calls the given function for each key/value pair in the cache.
-func (c *Cache[K, T]) ForEeach(f func(K, T)) {
+// If the function returns false, the iteration stops.
+func (c *Cache[K, T]) ForEeach(f func(K, T) bool) {
 	c.RLock()
 	defer c.RUnlock()
 	for k, v := range c.m {
-		f(k, v)
+		if !f(k, v) {
+			return
+		}
 	}
 }
 
diff --git a/common/paths/url.go b/common/paths/url.go
index 75b4b644a..867f68baf 100644
--- a/common/paths/url.go
+++ b/common/paths/url.go
@@ -1,4 +1,4 @@
-// Copyright 2021 The Hugo Authors. All rights reserved.
+// Copyright 2024 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ import (
 	"net/url"
 	"path"
 	"path/filepath"
+	"runtime"
 	"strings"
 )
 
@@ -159,9 +160,77 @@ func Uglify(in string) string {
 	return path.Clean(in)
 }
 
+// URLEscape escapes unicode letters.
+func URLEscape(uri string) string {
+	// escape unicode letters
+	u, err := url.Parse(uri)
+	if err != nil {
+		panic(err)
+	}
+	return u.String()
+}
+
+// TrimExt trims the extension from a path..
+func TrimExt(in string) string {
+	return strings.TrimSuffix(in, path.Ext(in))
+}
+
+// From https://github.com/golang/go/blob/e0c76d95abfc1621259864adb3d101cf6f1f90fc/src/cmd/go/internal/web/url.go#L45
+func UrlFromFilename(filename string) (*url.URL, error) {
+	if !filepath.IsAbs(filename) {
+		return nil, fmt.Errorf("filepath must be absolute")
+	}
+
+	// If filename has a Windows volume name, convert the volume to a host and prefix
+	// per https://blogs.msdn.microsoft.com/ie/2006/12/06/file-uris-in-windows/.
+	if vol := filepath.VolumeName(filename); vol != "" {
+		if strings.HasPrefix(vol, `\\`) {
+			filename = filepath.ToSlash(filename[2:])
+			i := strings.IndexByte(filename, '/')
+
+			if i < 0 {
+				// A degenerate case.
+				// \\host.example.com (without a share name)
+				// becomes
+				// file://host.example.com/
+				return &url.URL{
+					Scheme: "file",
+					Host:   filename,
+					Path:   "/",
+				}, nil
+			}
+
+			// \\host.example.com\Share\path\to\file
+			// becomes
+			// file://host.example.com/Share/path/to/file
+			return &url.URL{
+				Scheme: "file",
+				Host:   filename[:i],
+				Path:   filepath.ToSlash(filename[i:]),
+			}, nil
+		}
+
+		// C:\path\to\file
+		// becomes
+		// file:///C:/path/to/file
+		return &url.URL{
+			Scheme: "file",
+			Path:   "/" + filepath.ToSlash(filename),
+		}, nil
+	}
+
+	// /path/to/file
+	// becomes
+	// file:///path/to/file
+	return &url.URL{
+		Scheme: "file",
+		Path:   filepath.ToSlash(filename),
+	}, nil
+}
+
 // UrlToFilename converts the URL s to a filename.
 // If ParseRequestURI fails, the input is just converted to OS specific slashes and returned.
-func UrlToFilename(s string) (string, bool) {
+func UrlStringToFilename(s string) (string, bool) {
 	u, err := url.ParseRequestURI(s)
 	if err != nil {
 		return filepath.FromSlash(s), false
@@ -171,25 +240,34 @@ func UrlToFilename(s string) (string, bool) {
 
 	if p == "" {
 		p, _ = url.QueryUnescape(u.Opaque)
-		return filepath.FromSlash(p), true
+		return filepath.FromSlash(p), false
+	}
+
+	if runtime.GOOS != "windows" {
+		return p, true
+	}
+
+	if len(p) == 0 || p[0] != '/' {
+		return filepath.FromSlash(p), false
 	}
 
 	p = filepath.FromSlash(p)
 
-	if u.Host != "" {
-		// C:\data\file.txt
-		p = strings.ToUpper(u.Host) + ":" + p
+	if len(u.Host) == 1 {
+		// file://c/Users/...
+		return strings.ToUpper(u.Host) + ":" + p, true
 	}
 
-	return p, true
-}
+	if u.Host != "" && u.Host != "localhost" {
+		if filepath.VolumeName(u.Host) != "" {
+			return "", false
+		}
+		return `\\` + u.Host + p, true
+	}
 
-// URLEscape escapes unicode letters.
-func URLEscape(uri string) string {
-	// escape unicode letters
-	u, err := url.Parse(uri)
-	if err != nil {
-		panic(err)
+	if vol := filepath.VolumeName(p[1:]); vol == "" || strings.HasPrefix(vol, `\\`) {
+		return "", false
 	}
-	return u.String()
+
+	return p[1:], true
 }
diff --git a/common/types/closer.go b/common/types/closer.go
index 2844b1986..9f8875a8a 100644
--- a/common/types/closer.go
+++ b/common/types/closer.go
@@ -19,6 +19,13 @@ type Closer interface {
 	Close() error
 }
 
+// CloserFunc is a convenience type to create a Closer from a function.
+type CloserFunc func() error
+
+func (f CloserFunc) Close() error {
+	return f()
+}
+
 type CloseAdder interface {
 	Add(Closer)
 }
diff --git a/config/allconfig/configlanguage.go b/config/allconfig/configlanguage.go
index 38d2309ef..deec61449 100644
--- a/config/allconfig/configlanguage.go
+++ b/config/allconfig/configlanguage.go
@@ -137,11 +137,11 @@ func (c ConfigLanguage) Watching() bool {
 	return c.m.Base.Internal.Watch
 }
 
-func (c ConfigLanguage) NewIdentityManager(name string) identity.Manager {
+func (c ConfigLanguage) NewIdentityManager(name string, opts ...identity.ManagerOption) identity.Manager {
 	if !c.Watching() {
 		return identity.NopManager
 	}
-	return identity.NewManager(name)
+	return identity.NewManager(name, opts...)
 }
 
 func (c ConfigLanguage) ContentTypes() config.ContentTypesProvider {
diff --git a/config/configProvider.go b/config/configProvider.go
index ee6691cf1..5bda2c55a 100644
--- a/config/configProvider.go
+++ b/config/configProvider.go
@@ -58,7 +58,7 @@ type AllProvider interface {
 	BuildDrafts() bool
 	Running() bool
 	Watching() bool
-	NewIdentityManager(name string) identity.Manager
+	NewIdentityManager(name string, opts ...identity.ManagerOption) identity.Manager
 	FastRenderMode() bool
 	PrintUnusedTemplates() bool
 	EnableMissingTranslationPlaceholders() bool
diff --git a/deps/deps.go b/deps/deps.go
index 4389036cb..ca0f5ee3b 100644
--- a/deps/deps.go
+++ b/deps/deps.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"os"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -47,6 +48,9 @@ type Deps struct {
 	// The templates to use. This will usually implement the full tpl.TemplateManager.
 	tmplHandlers *tpl.TemplateHandlers
 
+	// The template funcs.
+	TmplFuncMap map[string]any
+
 	// The file systems to use.
 	Fs *hugofs.Fs `json:"-"`
 
@@ -83,10 +87,13 @@ type Deps struct {
 	Metrics metrics.Provider
 
 	// BuildStartListeners will be notified before a build starts.
-	BuildStartListeners *Listeners
+	BuildStartListeners *Listeners[any]
 
 	// BuildEndListeners will be notified after a build finishes.
-	BuildEndListeners *Listeners
+	BuildEndListeners *Listeners[any]
+
+	// OnChangeListeners will be notified when something changes.
+	OnChangeListeners *Listeners[identity.Identity]
 
 	// Resources that gets closed when the build is done or the server shuts down.
 	BuildClosers *types.Closers
@@ -154,17 +161,21 @@ func (d *Deps) Init() error {
 	}
 
 	if d.BuildStartListeners == nil {
-		d.BuildStartListeners = &Listeners{}
+		d.BuildStartListeners = &Listeners[any]{}
 	}
 
 	if d.BuildEndListeners == nil {
-		d.BuildEndListeners = &Listeners{}
+		d.BuildEndListeners = &Listeners[any]{}
 	}
 
 	if d.BuildClosers == nil {
 		d.BuildClosers = &types.Closers{}
 	}
 
+	if d.OnChangeListeners == nil {
+		d.OnChangeListeners = &Listeners[identity.Identity]{}
+	}
+
 	if d.Metrics == nil && d.Conf.TemplateMetrics() {
 		d.Metrics = metrics.NewProvider(d.Conf.TemplateMetricsHints())
 	}
@@ -268,6 +279,23 @@ func (d *Deps) Compile(prototype *Deps) error {
 	return nil
 }
 
+// MkdirTemp returns a temporary directory path that will be cleaned up on exit.
+func (d Deps) MkdirTemp(pattern string) (string, error) {
+	filename, err := os.MkdirTemp("", pattern)
+	if err != nil {
+		return "", err
+	}
+	d.BuildClosers.Add(
+		types.CloserFunc(
+			func() error {
+				return os.RemoveAll(filename)
+			},
+		),
+	)
+
+	return filename, nil
+}
+
 type globalErrHandler struct {
 	logger loggers.Logger
 
@@ -306,15 +334,16 @@ func (e *globalErrHandler) StopErrorCollector() {
 }
 
 // Listeners represents an event listener.
-type Listeners struct {
+type Listeners[T any] struct {
 	sync.Mutex
 
 	// A list of funcs to be notified about an event.
-	listeners []func()
+	// If the return value is true, the listener will be removed.
+	listeners []func(...T) bool
 }
 
 // Add adds a function to a Listeners instance.
-func (b *Listeners) Add(f func()) {
+func (b *Listeners[T]) Add(f func(...T) bool) {
 	if b == nil {
 		return
 	}
@@ -324,12 +353,16 @@ func (b *Listeners) Add(f func()) {
 }
 
 // Notify executes all listener functions.
-func (b *Listeners) Notify() {
+func (b *Listeners[T]) Notify(vs ...T) {
 	b.Lock()
 	defer b.Unlock()
+	temp := b.listeners[:0]
 	for _, notify := range b.listeners {
-		notify()
+		if !notify(vs...) {
+			temp = append(temp, notify)
+		}
 	}
+	b.listeners = temp
 }
 
 // ResourceProvider is used to create and refresh, and clone resources needed.
diff --git a/hugolib/content_map_page.go b/hugolib/content_map_page.go
index a336c8489..eda6f769e 100644
--- a/hugolib/content_map_page.go
+++ b/hugolib/content_map_page.go
@@ -1754,6 +1754,11 @@ func (sa *sitePagesAssembler) assembleResources() error {
 						mt = rs.rc.ContentMediaType
 					}
 
+					var filename string
+					if rs.fi != nil {
+						filename = rs.fi.Meta().Filename
+					}
+
 					rd := resources.ResourceSourceDescriptor{
 						OpenReadSeekCloser:   rs.opener,
 						Path:                 rs.path,
@@ -1762,6 +1767,7 @@ func (sa *sitePagesAssembler) assembleResources() error {
 						TargetBasePaths:      targetBasePaths,
 						BasePathRelPermalink: targetPaths.SubResourceBaseLink,
 						BasePathTargetPath:   baseTarget,
+						SourceFilenameOrPath: filename,
 						NameNormalized:       relPath,
 						NameOriginal:         relPathOriginal,
 						MediaType:            mt,
diff --git a/hugolib/hugo_sites.go b/hugolib/hugo_sites.go
index a5186fd44..792d6a990 100644
--- a/hugolib/hugo_sites.go
+++ b/hugolib/hugo_sites.go
@@ -111,6 +111,10 @@ func (h *HugoSites) ShouldSkipFileChangeEvent(ev fsnotify.Event) bool {
 	return h.skipRebuildForFilenames[ev.Name]
 }
 
+func (h *HugoSites) Close() error {
+	return h.Deps.Close()
+}
+
 func (h *HugoSites) isRebuild() bool {
 	return h.buildCounter.Load() > 0
 }
diff --git a/hugolib/hugo_sites_build.go b/hugolib/hugo_sites_build.go
index dd548be51..5346e2e6b 100644
--- a/hugolib/hugo_sites_build.go
+++ b/hugolib/hugo_sites_build.go
@@ -520,8 +520,9 @@ func (s *Site) executeDeferredTemplates(de *deps.DeferredExecutions) error {
 		},
 	})
 
-	de.FilenamesWithPostPrefix.ForEeach(func(filename string, _ bool) {
+	de.FilenamesWithPostPrefix.ForEeach(func(filename string, _ bool) bool {
 		g.Enqueue(filename)
+		return true
 	})
 
 	return g.Wait()
@@ -1058,6 +1059,8 @@ func (h *HugoSites) processPartialFileEvents(ctx context.Context, l logg.LevelLo
 		}
 	}
 
+	h.Deps.OnChangeListeners.Notify(changed.Changes()...)
+
 	if err := h.resolveAndClearStateForIdentities(ctx, l, cacheBusterOr, changed.Drain()); err != nil {
 		return err
 	}
diff --git a/hugolib/hugo_sites_build_errors_test.go b/hugolib/hugo_sites_build_errors_test.go
index 71afe6767..1298d7f4f 100644
--- a/hugolib/hugo_sites_build_errors_test.go
+++ b/hugolib/hugo_sites_build_errors_test.go
@@ -554,8 +554,6 @@ toc line 3
 toc line 4
 
 
-
-
 `
 
 	t.Run("base template", func(t *testing.T) {
@@ -569,7 +567,7 @@ toc line 4
 		).BuildE()
 
 		b.Assert(err, qt.IsNotNil)
-		b.Assert(err.Error(), qt.Contains, filepath.FromSlash(`render of "home" failed: "/layouts/baseof.html:4:6"`))
+		b.Assert(err.Error(), qt.Contains, `baseof.html:4:6`)
 	})
 
 	t.Run("index template", func(t *testing.T) {
@@ -583,7 +581,7 @@ toc line 4
 		).BuildE()
 
 		b.Assert(err, qt.IsNotNil)
-		b.Assert(err.Error(), qt.Contains, filepath.FromSlash(`render of "home" failed: "/layouts/index.html:3:7"`))
+		b.Assert(err.Error(), qt.Contains, `index.html:3:7"`)
 	})
 
 	t.Run("partial from define", func(t *testing.T) {
@@ -597,8 +595,7 @@ toc line 4
 		).BuildE()
 
 		b.Assert(err, qt.IsNotNil)
-		b.Assert(err.Error(), qt.Contains, filepath.FromSlash(`render of "home" failed: "/layouts/index.html:7:8": execute of template failed`))
-		b.Assert(err.Error(), qt.Contains, `execute of template failed: template: partials/toc.html:2:8: executing "partials/toc.html"`)
+		b.Assert(err.Error(), qt.Contains, `toc.html:2:8"`)
 	})
 }
 
diff --git a/hugolib/integrationtest_builder.go b/hugolib/integrationtest_builder.go
index 637e5dee0..bc83d65b3 100644
--- a/hugolib/integrationtest_builder.go
+++ b/hugolib/integrationtest_builder.go
@@ -69,6 +69,13 @@ func TestOptDebug() TestOpt {
 	}
 }
 
+// TestOptInfo will enable info logging in integration tests.
+func TestOptInfo() TestOpt {
+	return func(c *IntegrationTestConfig) {
+		c.LogLevel = logg.LevelInfo
+	}
+}
+
 // TestOptWarn will enable warn logging in integration tests.
 func TestOptWarn() TestOpt {
 	return func(c *IntegrationTestConfig) {
@@ -90,6 +97,13 @@ func TestOptWithNFDOnDarwin() TestOpt {
 	}
 }
 
+// TestOptWithOSFs enables the real file system.
+func TestOptWithOSFs() TestOpt {
+	return func(c *IntegrationTestConfig) {
+		c.NeedsOsFS = true
+	}
+}
+
 // TestOptWithWorkingDir allows setting any config optiona as a function al option.
 func TestOptWithConfig(fn func(c *IntegrationTestConfig)) TestOpt {
 	return func(c *IntegrationTestConfig) {
@@ -284,8 +298,9 @@ func (s *IntegrationTestBuilder) negate(match string) (string, bool) {
 func (s *IntegrationTestBuilder) AssertFileContent(filename string, matches ...string) {
 	s.Helper()
 	content := strings.TrimSpace(s.FileContent(filename))
+
 	for _, m := range matches {
-		cm := qt.Commentf("File: %s Match %s", filename, m)
+		cm := qt.Commentf("File: %s Match %s\nContent:\n%s", filename, m, content)
 		lines := strings.Split(m, "\n")
 		for _, match := range lines {
 			match = strings.TrimSpace(match)
@@ -313,7 +328,8 @@ func (s *IntegrationTestBuilder) AssertFileContentExact(filename string, matches
 	s.Helper()
 	content := s.FileContent(filename)
 	for _, m := range matches {
-		s.Assert(content, qt.Contains, m, qt.Commentf(m))
+		cm := qt.Commentf("File: %s Match %s\nContent:\n%s", filename, m, content)
+		s.Assert(content, qt.Contains, m, cm)
 	}
 }
 
@@ -450,6 +466,11 @@ func (s *IntegrationTestBuilder) Build() *IntegrationTestBuilder {
 	return s
 }
 
+func (s *IntegrationTestBuilder) Close() {
+	s.Helper()
+	s.Assert(s.H.Close(), qt.IsNil)
+}
+
 func (s *IntegrationTestBuilder) LogString() string {
 	return s.lastBuildLog
 }
diff --git a/hugolib/page.go b/hugolib/page.go
index e4c841966..83f0c6e25 100644
--- a/hugolib/page.go
+++ b/hugolib/page.go
@@ -143,6 +143,10 @@ func (p *pageState) GetDependencyManagerForScope(scope int) identity.Manager {
 	}
 }
 
+func (p *pageState) GetDependencyManagerForScopesAll() []identity.Manager {
+	return []identity.Manager{p.dependencyManager, p.dependencyManagerOutput}
+}
+
 func (p *pageState) Key() string {
 	return "page-" + strconv.FormatUint(p.pid, 10)
 }
diff --git a/hugolib/pages_capture.go b/hugolib/pages_capture.go
index 96c2c0f96..f175895c4 100644
--- a/hugolib/pages_capture.go
+++ b/hugolib/pages_capture.go
@@ -143,13 +143,29 @@ func (c *pagesCollector) Collect() (collectErr error) {
 			s.pageMap.cfg.isRebuild = true
 		}
 
+		var hasStructuralChange bool
+		for _, id := range c.ids {
+			if id.isStructuralChange() {
+				hasStructuralChange = true
+				break
+			}
+		}
+
 		for _, id := range c.ids {
 			if id.p.IsLeafBundle() {
 				collectErr = c.collectDir(
 					id.p,
 					false,
 					func(fim hugofs.FileMetaInfo) bool {
-						return true
+						if hasStructuralChange {
+							return true
+						}
+						fimp := fim.Meta().PathInfo
+						if fimp == nil {
+							return true
+						}
+
+						return fimp.Path() == id.p.Path()
 					},
 				)
 			} else if id.p.IsBranchBundle() {
diff --git a/hugolib/pagesfromdata/pagesfromgotmpl.go b/hugolib/pagesfromdata/pagesfromgotmpl.go
index fd7213bd9..2ee273718 100644
--- a/hugolib/pagesfromdata/pagesfromgotmpl.go
+++ b/hugolib/pagesfromdata/pagesfromgotmpl.go
@@ -245,10 +245,11 @@ func (b *BuildState) resolveDeletedPaths() {
 		return
 	}
 	var paths []string
-	b.sourceInfosPrevious.ForEeach(func(k string, _ *sourceInfo) {
+	b.sourceInfosPrevious.ForEeach(func(k string, _ *sourceInfo) bool {
 		if _, found := b.sourceInfosCurrent.Get(k); !found {
 			paths = append(paths, k)
 		}
+		return true
 	})
 
 	b.DeletedPaths = paths
@@ -287,6 +288,10 @@ func (p *PagesFromTemplate) GetDependencyManagerForScope(scope int) identity.Man
 	return p.DependencyManager
 }
 
+func (p *PagesFromTemplate) GetDependencyManagerForScopesAll() []identity.Manager {
+	return []identity.Manager{p.DependencyManager}
+}
+
 func (p *PagesFromTemplate) Execute(ctx context.Context) (BuildInfo, error) {
 	defer func() {
 		p.buildState.PrepareNextBuild()
diff --git a/hugolib/rebuild_test.go b/hugolib/rebuild_test.go
index ff1f8267e..42e1b8ed5 100644
--- a/hugolib/rebuild_test.go
+++ b/hugolib/rebuild_test.go
@@ -98,6 +98,18 @@ My Other Text: {{ $r.Content }}|{{ $r.Permalink }}|
 
 `
 
+func TestRebuildEditLeafBundleHeaderOnly(t *testing.T) {
+	b := TestRunning(t, rebuildFilesSimple)
+	b.AssertFileContent("public/mysection/mysectionbundle/index.html",
+		"My Section Bundle Content Content.")
+
+	b.EditFileReplaceAll("content/mysection/mysectionbundle/index.md", "My Section Bundle Content.", "My Section Bundle Content Edited.").Build()
+	b.AssertFileContent("public/mysection/mysectionbundle/index.html",
+		"My Section Bundle Content Edited.")
+	b.AssertRenderCountPage(2) // home (rss) + bundle.
+	b.AssertRenderCountContent(1)
+}
+
 func TestRebuildEditTextFileInLeafBundle(t *testing.T) {
 	b := TestRunning(t, rebuildFilesSimple)
 	b.AssertFileContent("public/mysection/mysectionbundle/index.html",
@@ -962,7 +974,7 @@ Single. {{ partial "head.html" . }}$
 RelPermalink: {{ $js.RelPermalink }}|
 `
 
-	b := TestRunning(t, files)
+	b := TestRunning(t, files, TestOptOsFs())
 
 	b.AssertFileContent("public/p1/index.html", "/js/main.712a50b59d0f0dedb4e3606eaa3860b1f1a5305f6c42da30a2985e473ba314eb.js")
 	b.AssertFileContent("public/index.html", "/js/main.712a50b59d0f0dedb4e3606eaa3860b1f1a5305f6c42da30a2985e473ba314eb.js")
@@ -998,7 +1010,7 @@ Base. {{ partial "common/head.html" . }}$
 RelPermalink: {{ $js.RelPermalink }}|
 `
 
-	b := TestRunning(t, files)
+	b := TestRunning(t, files, TestOptOsFs())
 
 	b.AssertFileContent("public/index.html", "/js/main.712a50b59d0f0dedb4e3606eaa3860b1f1a5305f6c42da30a2985e473ba314eb.js")
 
diff --git a/hugolib/site.go b/hugolib/site.go
index f6dc89a77..7ec70eb6c 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -1493,7 +1493,11 @@ func (s *Site) renderForTemplate(ctx context.Context, name, outputFormat string,
 	}
 
 	if err = s.Tmpl().ExecuteWithContext(ctx, templ, w, d); err != nil {
-		return fmt.Errorf("render of %q failed: %w", name, err)
+		filename := name
+		if p, ok := d.(*pageState); ok {
+			filename = p.String()
+		}
+		return fmt.Errorf("render of %q failed: %w", filename, err)
 	}
 	return
 }
diff --git a/identity/identity.go b/identity/identity.go
index d106eb1fc..e38a8f0f2 100644
--- a/identity/identity.go
+++ b/identity/identity.go
@@ -82,9 +82,8 @@ func FirstIdentity(v any) Identity {
 	var result Identity = Anonymous
 	WalkIdentitiesShallow(v, func(level int, id Identity) bool {
 		result = id
-		return true
+		return result != Anonymous
 	})
-
 	return result
 }
 
@@ -146,6 +145,7 @@ func (d DependencyManagerProviderFunc) GetDependencyManager() Manager {
 // DependencyManagerScopedProvider provides a manager for dependencies with a given scope.
 type DependencyManagerScopedProvider interface {
 	GetDependencyManagerForScope(scope int) Manager
+	GetDependencyManagerForScopesAll() []Manager
 }
 
 // ForEeachIdentityProvider provides a way iterate over identities.
@@ -308,11 +308,13 @@ type identityManager struct {
 
 func (im *identityManager) AddIdentity(ids ...Identity) {
 	im.mu.Lock()
+	defer im.mu.Unlock()
 
 	for _, id := range ids {
 		if id == nil || id == Anonymous {
 			continue
 		}
+
 		if _, found := im.ids[id]; !found {
 			if im.onAddIdentity != nil {
 				im.onAddIdentity(id)
@@ -320,7 +322,6 @@ func (im *identityManager) AddIdentity(ids ...Identity) {
 			im.ids[id] = true
 		}
 	}
-	im.mu.Unlock()
 }
 
 func (im *identityManager) AddIdentityForEach(ids ...ForEeachIdentityProvider) {
@@ -355,6 +356,10 @@ func (im *identityManager) GetDependencyManagerForScope(int) Manager {
 	return im
 }
 
+func (im *identityManager) GetDependencyManagerForScopesAll() []Manager {
+	return []Manager{im}
+}
+
 func (im *identityManager) String() string {
 	return fmt.Sprintf("IdentityManager(%s)", im.name)
 }
diff --git a/internal/js/esbuild/batch-esm-runner.gotmpl b/internal/js/esbuild/batch-esm-runner.gotmpl
new file mode 100644
index 000000000..3193b4c30
--- /dev/null
+++ b/internal/js/esbuild/batch-esm-runner.gotmpl
@@ -0,0 +1,20 @@
+{{ range $i, $e := .Scripts -}}
+  {{ if eq .Export "*" }}
+    {{- printf "import %s as Script%d from %q;" .Export $i .Import -}}
+  {{ else -}}
+    {{- printf "import { %s as Script%d } from %q;" .Export $i .Import -}}
+  {{ end -}}
+{{ end -}}
+{{ range $i, $e := .Runners }}
+  {{- printf "import { %s as Run%d } from %q;" .Export $i .Import -}}
+{{ end -}}
+{{ if  .Runners -}}
+  let group = { id: "{{ $.ID }}", scripts: [] }
+  {{ range $i, $e := .Scripts -}}
+    group.scripts.push({{ .RunnerJSON $i }});
+  {{ end -}}
+  {{ range $i, $e := .Runners -}}
+    {{ $id := printf "Run%d" $i }}
+    {{ $id }}(group);
+  {{ end -}}
+{{ end -}}
diff --git a/internal/js/esbuild/batch.go b/internal/js/esbuild/batch.go
new file mode 100644
index 000000000..43e2da444
--- /dev/null
+++ b/internal/js/esbuild/batch.go
@@ -0,0 +1,1437 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package esbuild provides functions for building JavaScript resources.
+package esbuild
+
+import (
+	"bytes"
+	"context"
+	_ "embed"
+	"encoding/json"
+	"fmt"
+	"path"
+	"path/filepath"
+	"reflect"
+	"sort"
+	"strings"
+	"sync"
+	"sync/atomic"
+
+	"github.com/evanw/esbuild/pkg/api"
+	"github.com/gohugoio/hugo/cache/dynacache"
+	"github.com/gohugoio/hugo/common/hugio"
+	"github.com/gohugoio/hugo/common/maps"
+	"github.com/gohugoio/hugo/common/paths"
+	"github.com/gohugoio/hugo/deps"
+	"github.com/gohugoio/hugo/identity"
+	"github.com/gohugoio/hugo/lazy"
+	"github.com/gohugoio/hugo/media"
+	"github.com/gohugoio/hugo/resources"
+	"github.com/gohugoio/hugo/resources/resource"
+	"github.com/gohugoio/hugo/resources/resource_factories/create"
+	"github.com/gohugoio/hugo/tpl"
+	"github.com/mitchellh/mapstructure"
+	"github.com/spf13/afero"
+	"github.com/spf13/cast"
+)
+
+var _ Batcher = (*batcher)(nil)
+
+const (
+	NsBatch = "_hugo-js-batch"
+
+	propsKeyImportContext = "importContext"
+	propsResoure          = "resource"
+)
+
+//go:embed batch-esm-runner.gotmpl
+var runnerTemplateStr string
+
+var _ BatchPackage = (*Package)(nil)
+
+var _ buildToucher = (*optsHolder[scriptOptions])(nil)
+
+var (
+	_ buildToucher             = (*scriptGroup)(nil)
+	_ isBuiltOrTouchedProvider = (*scriptGroup)(nil)
+)
+
+func NewBatcherClient(deps *deps.Deps) (*BatcherClient, error) {
+	c := &BatcherClient{
+		d:            deps,
+		buildClient:  NewBuildClient(deps.BaseFs.Assets, deps.ResourceSpec),
+		createClient: create.New(deps.ResourceSpec),
+		bundlesCache: maps.NewCache[string, BatchPackage](),
+	}
+
+	deps.BuildEndListeners.Add(func(...any) bool {
+		c.bundlesCache.Reset()
+		return false
+	})
+
+	return c, nil
+}
+
+func (o optionsMap[K, C]) ByKey() optionsGetSetters[K, C] {
+	var values []optionsGetSetter[K, C]
+	for _, v := range o {
+		values = append(values, v)
+	}
+
+	sort.Slice(values, func(i, j int) bool {
+		return values[i].Key().String() < values[j].Key().String()
+	})
+
+	return values
+}
+
+func (o *opts[K, C]) Compiled() C {
+	o.h.checkCompileErr()
+	return o.h.compiled
+}
+
+func (os optionsGetSetters[K, C]) Filter(predicate func(K) bool) optionsGetSetters[K, C] {
+	var a optionsGetSetters[K, C]
+	for _, v := range os {
+		if predicate(v.Key()) {
+			a = append(a, v)
+		}
+	}
+	return a
+}
+
+func (o *optsHolder[C]) IdentifierBase() string {
+	return o.optionsID
+}
+
+func (o *opts[K, C]) Key() K {
+	return o.key
+}
+
+func (o *opts[K, C]) Reset() {
+	mu := o.once.ResetWithLock()
+	defer mu.Unlock()
+	o.h.resetCounter++
+}
+
+func (o *opts[K, C]) Get(id uint32) OptionsSetter {
+	var b *optsHolder[C]
+	o.once.Do(func() {
+		b = o.h
+		b.setBuilt(id)
+	})
+	return b
+}
+
+func (o *opts[K, C]) GetIdentity() identity.Identity {
+	return o.h
+}
+
+func (o *optsHolder[C]) SetOptions(m map[string]any) string {
+	o.optsSetCounter++
+	o.optsPrev = o.optsCurr
+	o.optsCurr = m
+	o.compiledPrev = o.compiled
+	o.compiled, o.compileErr = o.compiled.compileOptions(m, o.defaults)
+	o.checkCompileErr()
+	return ""
+}
+
+// ValidateBatchID validates the given ID according to some very
+func ValidateBatchID(id string, isTopLevel bool) error {
+	if id == "" {
+		return fmt.Errorf("id must be set")
+	}
+	// No Windows slashes.
+	if strings.Contains(id, "\\") {
+		return fmt.Errorf("id must not contain backslashes")
+	}
+
+	// Allow forward slashes in top level IDs only.
+	if !isTopLevel && strings.Contains(id, "/") {
+		return fmt.Errorf("id must not contain forward slashes")
+	}
+
+	return nil
+}
+
+func newIsBuiltOrTouched() isBuiltOrTouched {
+	return isBuiltOrTouched{
+		built:   make(buildIDs),
+		touched: make(buildIDs),
+	}
+}
+
+func newOpts[K any, C optionsCompiler[C]](key K, optionsID string, defaults defaultOptionValues) *opts[K, C] {
+	return &opts[K, C]{
+		key: key,
+		h: &optsHolder[C]{
+			optionsID:        optionsID,
+			defaults:         defaults,
+			isBuiltOrTouched: newIsBuiltOrTouched(),
+		},
+	}
+}
+
+// BatchPackage holds a group of JavaScript resources.
+type BatchPackage interface {
+	Groups() map[string]resource.Resources
+}
+
+// Batcher is used to build JavaScript packages.
+type Batcher interface {
+	Build(context.Context) (BatchPackage, error)
+	Config(ctx context.Context) OptionsSetter
+	Group(ctx context.Context, id string) BatcherGroup
+}
+
+// BatcherClient is a client for building JavaScript packages.
+type BatcherClient struct {
+	d *deps.Deps
+
+	once           sync.Once
+	runnerTemplate tpl.Template
+
+	createClient *create.Client
+	buildClient  *BuildClient
+
+	bundlesCache *maps.Cache[string, BatchPackage]
+}
+
+// New creates a new Batcher with the given ID.
+// This will be typically created once and reused across rebuilds.
+func (c *BatcherClient) New(id string) (Batcher, error) {
+	var initErr error
+	c.once.Do(func() {
+		// We should fix the initialization order here (or use the Go template package directly), but we need to wait
+		// for the Hugo templates to be ready.
+		tmpl, err := c.d.TextTmpl().Parse("batch-esm-runner", runnerTemplateStr)
+		if err != nil {
+			initErr = err
+			return
+		}
+		c.runnerTemplate = tmpl
+	})
+
+	if initErr != nil {
+		return nil, initErr
+	}
+
+	dependencyManager := c.d.Conf.NewIdentityManager("jsbatch_" + id)
+	configID := "config_" + id
+
+	b := &batcher{
+		id:                id,
+		scriptGroups:      make(map[string]*scriptGroup),
+		dependencyManager: dependencyManager,
+		client:            c,
+		configOptions: newOpts[scriptID, configOptions](
+			scriptID(configID),
+			configID,
+			defaultOptionValues{},
+		),
+	}
+
+	c.d.BuildEndListeners.Add(func(...any) bool {
+		b.reset()
+		return false
+	})
+
+	idFinder := identity.NewFinder(identity.FinderConfig{})
+
+	c.d.OnChangeListeners.Add(func(ids ...identity.Identity) bool {
+		for _, id := range ids {
+			if r := idFinder.Contains(id, b.dependencyManager, 50); r > 0 {
+				b.staleVersion.Add(1)
+				return false
+			}
+
+			sp, ok := id.(identity.DependencyManagerScopedProvider)
+			if !ok {
+				continue
+			}
+			idms := sp.GetDependencyManagerForScopesAll()
+
+			for _, g := range b.scriptGroups {
+				g.forEachIdentity(func(id2 identity.Identity) bool {
+					bt, ok := id2.(buildToucher)
+					if !ok {
+						return false
+					}
+					for _, id3 := range idms {
+						// This handles the removal of the only source for a script group (e.g. all shortcodes in a contnt page).
+						// Note the very shallow search.
+						if r := idFinder.Contains(id2, id3, 0); r > 0 {
+							bt.setTouched(b.buildCount)
+							return false
+						}
+					}
+					return false
+				})
+			}
+		}
+
+		return false
+	})
+
+	return b, nil
+}
+
+func (c *BatcherClient) buildBatchGroup(ctx context.Context, t *batchGroupTemplateContext) (resource.Resource, string, error) {
+	var buf bytes.Buffer
+
+	if err := c.d.Tmpl().ExecuteWithContext(ctx, c.runnerTemplate, &buf, t); err != nil {
+		return nil, "", err
+	}
+
+	s := paths.AddLeadingSlash(t.keyPath + ".js")
+	r, err := c.createClient.FromString(s, buf.String())
+	if err != nil {
+		return nil, "", err
+	}
+
+	return r, s, nil
+}
+
+// BatcherGroup is a group of scripts and instances.
+type BatcherGroup interface {
+	Instance(sid, iid string) OptionsSetter
+	Runner(id string) OptionsSetter
+	Script(id string) OptionsSetter
+}
+
+// OptionsSetter is used to set options for a batch, script or instance.
+type OptionsSetter interface {
+	SetOptions(map[string]any) string
+}
+
+// Package holds a group of JavaScript resources.
+type Package struct {
+	id string
+	b  *batcher
+
+	groups map[string]resource.Resources
+}
+
+func (p *Package) Groups() map[string]resource.Resources {
+	return p.groups
+}
+
+type batchGroupTemplateContext struct {
+	keyPath string
+	ID      string
+	Runners []scriptRunnerTemplateContext
+	Scripts []scriptBatchTemplateContext
+}
+
+type batcher struct {
+	mu           sync.Mutex
+	id           string
+	buildCount   uint32
+	staleVersion atomic.Uint32
+	scriptGroups scriptGroups
+
+	client            *BatcherClient
+	dependencyManager identity.Manager
+
+	configOptions optionsGetSetter[scriptID, configOptions]
+
+	// The last successfully built package.
+	// If this is non-nil and not stale, we can reuse it (e.g. on server rebuilds)
+	prevBuild *Package
+}
+
+// Build builds the batch if not already built or if it's stale.
+func (b *batcher) Build(ctx context.Context) (BatchPackage, error) {
+	key := dynacache.CleanKey(b.id + ".js")
+	p, err := b.client.bundlesCache.GetOrCreate(key, func() (BatchPackage, error) {
+		return b.build(ctx)
+	})
+	if err != nil {
+		return nil, fmt.Errorf("failed to build JS batch %q: %w", b.id, err)
+	}
+	return p, nil
+}
+
+func (b *batcher) Config(ctx context.Context) OptionsSetter {
+	return b.configOptions.Get(b.buildCount)
+}
+
+func (b *batcher) Group(ctx context.Context, id string) BatcherGroup {
+	if err := ValidateBatchID(id, false); err != nil {
+		panic(err)
+	}
+
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	group, found := b.scriptGroups[id]
+	if !found {
+		idm := b.client.d.Conf.NewIdentityManager("jsbatch_" + id)
+		b.dependencyManager.AddIdentity(idm)
+
+		group = &scriptGroup{
+			id: id, b: b,
+			isBuiltOrTouched:  newIsBuiltOrTouched(),
+			dependencyManager: idm,
+			scriptsOptions:    make(optionsMap[scriptID, scriptOptions]),
+			instancesOptions:  make(optionsMap[instanceID, paramsOptions]),
+			runnersOptions:    make(optionsMap[scriptID, scriptOptions]),
+		}
+		b.scriptGroups[id] = group
+	}
+
+	group.setBuilt(b.buildCount)
+
+	return group
+}
+
+func (b *batcher) isStale() bool {
+	if b.staleVersion.Load() > 0 {
+		return true
+	}
+
+	if b.removeNotSet() {
+		return true
+	}
+
+	if b.configOptions.isStale() {
+		return true
+	}
+
+	for _, v := range b.scriptGroups {
+		if v.isStale() {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (b *batcher) build(ctx context.Context) (BatchPackage, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	defer func() {
+		b.staleVersion.Store(0)
+		b.buildCount++
+	}()
+
+	if b.prevBuild != nil {
+		if !b.isStale() {
+			return b.prevBuild, nil
+		}
+	}
+
+	p, err := b.doBuild(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	b.prevBuild = p
+
+	return p, nil
+}
+
+func (b *batcher) doBuild(ctx context.Context) (*Package, error) {
+	type importContext struct {
+		name           string
+		resourceGetter resource.ResourceGetter
+		scriptOptions  scriptOptions
+		dm             identity.Manager
+	}
+
+	state := struct {
+		importResource        *maps.Cache[string, resource.Resource]
+		resultResource        *maps.Cache[string, resource.Resource]
+		importerImportContext *maps.Cache[string, importContext]
+		pathGroup             *maps.Cache[string, string]
+	}{
+		importResource:        maps.NewCache[string, resource.Resource](),
+		resultResource:        maps.NewCache[string, resource.Resource](),
+		importerImportContext: maps.NewCache[string, importContext](),
+		pathGroup:             maps.NewCache[string, string](),
+	}
+
+	// Entry points passed to ESBuid.
+	var entryPoints []string
+	addResource := func(group, pth string, r resource.Resource, isResult bool) {
+		state.pathGroup.Set(paths.TrimExt(pth), group)
+		state.importResource.Set(pth, r)
+		if isResult {
+			state.resultResource.Set(pth, r)
+		}
+		entryPoints = append(entryPoints, pth)
+	}
+
+	for k, v := range b.scriptGroups {
+		keyPath := k
+		var runners []scriptRunnerTemplateContext
+		for _, vv := range v.runnersOptions.ByKey() {
+			runnerKeyPath := keyPath + "_" + vv.Key().String()
+			runnerImpPath := paths.AddLeadingSlash(runnerKeyPath + "_runner" + vv.Compiled().Resource.MediaType().FirstSuffix.FullSuffix)
+			runners = append(runners, scriptRunnerTemplateContext{opts: vv, Import: runnerImpPath})
+			addResource(k, runnerImpPath, vv.Compiled().Resource, false)
+		}
+
+		t := &batchGroupTemplateContext{
+			keyPath: keyPath,
+			ID:      v.id,
+			Runners: runners,
+		}
+
+		instances := v.instancesOptions.ByKey()
+
+		for _, vv := range v.scriptsOptions.ByKey() {
+			keyPath := keyPath + "_" + vv.Key().String()
+			opts := vv.Compiled()
+			impPath := path.Join(PrefixHugoVirtual, opts.Dir(), keyPath+opts.Resource.MediaType().FirstSuffix.FullSuffix)
+			impCtx := opts.ImportContext
+
+			state.importerImportContext.Set(impPath, importContext{
+				name:           keyPath,
+				resourceGetter: impCtx,
+				scriptOptions:  opts,
+				dm:             v.dependencyManager,
+			})
+
+			bt := scriptBatchTemplateContext{
+				opts:   vv,
+				Import: impPath,
+			}
+			state.importResource.Set(bt.Import, vv.Compiled().Resource)
+			predicate := func(k instanceID) bool {
+				return k.scriptID == vv.Key()
+			}
+			for _, vvv := range instances.Filter(predicate) {
+				bt.Instances = append(bt.Instances, scriptInstanceBatchTemplateContext{opts: vvv})
+			}
+
+			t.Scripts = append(t.Scripts, bt)
+		}
+
+		r, s, err := b.client.buildBatchGroup(ctx, t)
+		if err != nil {
+			return nil, fmt.Errorf("failed to build JS batch: %w", err)
+		}
+
+		state.importerImportContext.Set(s, importContext{
+			name:           s,
+			resourceGetter: nil,
+			dm:             v.dependencyManager,
+		})
+
+		addResource(v.id, s, r, true)
+	}
+
+	mediaTypes := b.client.d.ResourceSpec.MediaTypes()
+
+	externalOptions := b.configOptions.Compiled().Options
+	if externalOptions.Format == "" {
+		externalOptions.Format = "esm"
+	}
+	if externalOptions.Format != "esm" {
+		return nil, fmt.Errorf("only esm format is currently supported")
+	}
+
+	jsOpts := Options{
+		ExternalOptions: externalOptions,
+		InternalOptions: InternalOptions{
+			DependencyManager: b.dependencyManager,
+			Splitting:         true,
+			ImportOnResolveFunc: func(imp string, args api.OnResolveArgs) string {
+				var importContextPath string
+				if args.Kind == api.ResolveEntryPoint {
+					importContextPath = args.Path
+				} else {
+					importContextPath = args.Importer
+				}
+				importContext, importContextFound := state.importerImportContext.Get(importContextPath)
+
+				// We want to track the dependencies closest to where they're used.
+				dm := b.dependencyManager
+				if importContextFound {
+					dm = importContext.dm
+				}
+
+				if r, found := state.importResource.Get(imp); found {
+					dm.AddIdentity(identity.FirstIdentity(r))
+					return imp
+				}
+
+				if importContext.resourceGetter != nil {
+					resolved := ResolveResource(imp, importContext.resourceGetter)
+					if resolved != nil {
+						resolvePath := resources.InternalResourceTargetPath(resolved)
+						dm.AddIdentity(identity.FirstIdentity(resolved))
+						imp := PrefixHugoVirtual + resolvePath
+						state.importResource.Set(imp, resolved)
+						state.importerImportContext.Set(imp, importContext)
+						return imp
+
+					}
+				}
+				return ""
+			},
+			ImportOnLoadFunc: func(args api.OnLoadArgs) string {
+				imp := args.Path
+
+				if r, found := state.importResource.Get(imp); found {
+					content, err := r.(resource.ContentProvider).Content(ctx)
+					if err != nil {
+						panic(err)
+					}
+					return cast.ToString(content)
+				}
+				return ""
+			},
+			ImportParamsOnLoadFunc: func(args api.OnLoadArgs) json.RawMessage {
+				if importContext, found := state.importerImportContext.Get(args.Path); found {
+					if !importContext.scriptOptions.IsZero() {
+						return importContext.scriptOptions.Params
+					}
+				}
+				return nil
+			},
+			ErrorMessageResolveFunc: func(args api.Message) *ErrorMessageResolved {
+				if loc := args.Location; loc != nil {
+					path := strings.TrimPrefix(loc.File, NsHugoImportResolveFunc+":")
+					if r, found := state.importResource.Get(path); found {
+						sourcePath := resources.InternalResourceSourcePathBestEffort(r)
+
+						var contentr hugio.ReadSeekCloser
+						if cp, ok := r.(hugio.ReadSeekCloserProvider); ok {
+							contentr, _ = cp.ReadSeekCloser()
+						}
+						return &ErrorMessageResolved{
+							Content: contentr,
+							Path:    sourcePath,
+							Message: args.Text,
+						}
+
+					}
+
+				}
+				return nil
+			},
+			ResolveSourceMapSource: func(s string) string {
+				if r, found := state.importResource.Get(s); found {
+					if ss := resources.InternalResourceSourcePath(r); ss != "" {
+						return ss
+					}
+					return PrefixHugoMemory + s
+				}
+				return ""
+			},
+			EntryPoints: entryPoints,
+		},
+	}
+
+	result, err := b.client.buildClient.Build(jsOpts)
+	if err != nil {
+		return nil, fmt.Errorf("failed to build JS bundle: %w", err)
+	}
+
+	groups := make(map[string]resource.Resources)
+
+	createAndAddResource := func(targetPath, group string, o api.OutputFile, mt media.Type) error {
+		var sourceFilename string
+		if r, found := state.importResource.Get(targetPath); found {
+			sourceFilename = resources.InternalResourceSourcePathBestEffort(r)
+		}
+		targetPath = path.Join(b.id, targetPath)
+
+		rd := resources.ResourceSourceDescriptor{
+			LazyPublish: true,
+			OpenReadSeekCloser: func() (hugio.ReadSeekCloser, error) {
+				return hugio.NewReadSeekerNoOpCloserFromBytes(o.Contents), nil
+			},
+			MediaType:            mt,
+			TargetPath:           targetPath,
+			SourceFilenameOrPath: sourceFilename,
+		}
+		r, err := b.client.d.ResourceSpec.NewResource(rd)
+		if err != nil {
+			return err
+		}
+
+		groups[group] = append(groups[group], r)
+
+		return nil
+	}
+
+	outDir := b.client.d.AbsPublishDir
+
+	createAndAddResources := func(o api.OutputFile) (bool, error) {
+		p := paths.ToSlashPreserveLeading(strings.TrimPrefix(o.Path, outDir))
+		ext := path.Ext(p)
+		mt, _, found := mediaTypes.GetBySuffix(ext)
+		if !found {
+			return false, nil
+		}
+
+		group, found := state.pathGroup.Get(paths.TrimExt(p))
+
+		if !found {
+			return false, nil
+		}
+
+		if err := createAndAddResource(p, group, o, mt); err != nil {
+			return false, err
+		}
+
+		return true, nil
+	}
+
+	for _, o := range result.OutputFiles {
+		handled, err := createAndAddResources(o)
+		if err != nil {
+			return nil, err
+		}
+
+		if !handled {
+			//  Copy to destination.
+			p := strings.TrimPrefix(o.Path, outDir)
+			targetFilename := filepath.Join(b.id, p)
+			fs := b.client.d.BaseFs.PublishFs
+			if err := fs.MkdirAll(filepath.Dir(targetFilename), 0o777); err != nil {
+				return nil, fmt.Errorf("failed to create dir %q: %w", targetFilename, err)
+			}
+
+			if err := afero.WriteFile(fs, targetFilename, o.Contents, 0o666); err != nil {
+				return nil, fmt.Errorf("failed to write to %q: %w", targetFilename, err)
+			}
+		}
+	}
+
+	p := &Package{
+		id:     path.Join(NsBatch, b.id),
+		b:      b,
+		groups: groups,
+	}
+
+	return p, nil
+}
+
+func (b *batcher) removeNotSet() bool {
+	// We already have the lock.
+	var removed bool
+	currentBuildID := b.buildCount
+	for k, v := range b.scriptGroups {
+		if !v.isBuilt(currentBuildID) && v.isTouched(currentBuildID) {
+			// Remove entire group.
+			removed = true
+			delete(b.scriptGroups, k)
+			continue
+		}
+		if v.removeTouchedButNotSet() {
+			removed = true
+		}
+		if v.removeNotSet() {
+			removed = true
+		}
+	}
+
+	return removed
+}
+
+func (b *batcher) reset() {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.configOptions.Reset()
+	for _, v := range b.scriptGroups {
+		v.Reset()
+	}
+}
+
+type buildIDs map[uint32]bool
+
+func (b buildIDs) Has(buildID uint32) bool {
+	return b[buildID]
+}
+
+func (b buildIDs) Set(buildID uint32) {
+	b[buildID] = true
+}
+
+type buildToucher interface {
+	setTouched(buildID uint32)
+}
+
+type configOptions struct {
+	Options ExternalOptions
+}
+
+func (s configOptions) isStaleCompiled(prev configOptions) bool {
+	return false
+}
+
+func (s configOptions) compileOptions(m map[string]any, defaults defaultOptionValues) (configOptions, error) {
+	config, err := DecodeExternalOptions(m)
+	if err != nil {
+		return configOptions{}, err
+	}
+
+	return configOptions{
+		Options: config,
+	}, nil
+}
+
+type defaultOptionValues struct {
+	defaultExport string
+}
+
+type instanceID struct {
+	scriptID   scriptID
+	instanceID string
+}
+
+func (i instanceID) String() string {
+	return i.scriptID.String() + "_" + i.instanceID
+}
+
+type isBuiltOrTouched struct {
+	built   buildIDs
+	touched buildIDs
+}
+
+func (i isBuiltOrTouched) setBuilt(id uint32) {
+	i.built.Set(id)
+}
+
+func (i isBuiltOrTouched) isBuilt(id uint32) bool {
+	return i.built.Has(id)
+}
+
+func (i isBuiltOrTouched) setTouched(id uint32) {
+	i.touched.Set(id)
+}
+
+func (i isBuiltOrTouched) isTouched(id uint32) bool {
+	return i.touched.Has(id)
+}
+
+type isBuiltOrTouchedProvider interface {
+	isBuilt(uint32) bool
+	isTouched(uint32) bool
+}
+
+type key interface {
+	comparable
+	fmt.Stringer
+}
+
+type optionsCompiler[C any] interface {
+	isStaleCompiled(C) bool
+	compileOptions(map[string]any, defaultOptionValues) (C, error)
+}
+
+type optionsGetSetter[K, C any] interface {
+	isBuiltOrTouchedProvider
+	identity.IdentityProvider
+	// resource.StaleInfo
+
+	Compiled() C
+	Key() K
+	Reset()
+
+	Get(uint32) OptionsSetter
+	isStale() bool
+	currPrev() (map[string]any, map[string]any)
+}
+
+type optionsGetSetters[K key, C any] []optionsGetSetter[K, C]
+
+type optionsMap[K key, C any] map[K]optionsGetSetter[K, C]
+
+type opts[K any, C optionsCompiler[C]] struct {
+	key  K
+	h    *optsHolder[C]
+	once lazy.OnceMore
+}
+
+type optsHolder[C optionsCompiler[C]] struct {
+	optionsID string
+
+	defaults defaultOptionValues
+
+	// Keep track of one generation so we can detect changes.
+	// Note that most of this tracking is performed on the options/map level.
+	compiled     C
+	compiledPrev C
+	compileErr   error
+
+	resetCounter   uint32
+	optsSetCounter uint32
+	optsCurr       map[string]any
+	optsPrev       map[string]any
+
+	isBuiltOrTouched
+}
+
+type paramsOptions struct {
+	Params json.RawMessage
+}
+
+func (s paramsOptions) isStaleCompiled(prev paramsOptions) bool {
+	return false
+}
+
+func (s paramsOptions) compileOptions(m map[string]any, defaults defaultOptionValues) (paramsOptions, error) {
+	v := struct {
+		Params map[string]any
+	}{}
+
+	if err := mapstructure.WeakDecode(m, &v); err != nil {
+		return paramsOptions{}, err
+	}
+
+	paramsJSON, err := json.Marshal(v.Params)
+	if err != nil {
+		return paramsOptions{}, err
+	}
+
+	return paramsOptions{
+		Params: paramsJSON,
+	}, nil
+}
+
+type scriptBatchTemplateContext struct {
+	opts      optionsGetSetter[scriptID, scriptOptions]
+	Import    string
+	Instances []scriptInstanceBatchTemplateContext
+}
+
+func (s *scriptBatchTemplateContext) Export() string {
+	return s.opts.Compiled().Export
+}
+
+func (c scriptBatchTemplateContext) MarshalJSON() (b []byte, err error) {
+	return json.Marshal(&struct {
+		ID        string                               `json:"id"`
+		Instances []scriptInstanceBatchTemplateContext `json:"instances"`
+	}{
+		ID:        c.opts.Key().String(),
+		Instances: c.Instances,
+	})
+}
+
+func (b scriptBatchTemplateContext) RunnerJSON(i int) string {
+	script := fmt.Sprintf("Script%d", i)
+
+	v := struct {
+		ID string `json:"id"`
+
+		// Read-only live JavaScript binding.
+		Binding   string                               `json:"binding"`
+		Instances []scriptInstanceBatchTemplateContext `json:"instances"`
+	}{
+		b.opts.Key().String(),
+		script,
+		b.Instances,
+	}
+
+	bb, err := json.Marshal(v)
+	if err != nil {
+		panic(err)
+	}
+	s := string(bb)
+
+	// Remove the quotes to make it a valid JS object.
+	s = strings.ReplaceAll(s, fmt.Sprintf("%q", script), script)
+
+	return s
+}
+
+type scriptGroup struct {
+	mu sync.Mutex
+	id string
+	b  *batcher
+	isBuiltOrTouched
+	dependencyManager identity.Manager
+
+	scriptsOptions   optionsMap[scriptID, scriptOptions]
+	instancesOptions optionsMap[instanceID, paramsOptions]
+	runnersOptions   optionsMap[scriptID, scriptOptions]
+}
+
+// For internal use only.
+func (b *scriptGroup) GetDependencyManager() identity.Manager {
+	return b.dependencyManager
+}
+
+// For internal use only.
+func (b *scriptGroup) IdentifierBase() string {
+	return b.id
+}
+
+func (s *scriptGroup) Instance(sid, id string) OptionsSetter {
+	if err := ValidateBatchID(sid, false); err != nil {
+		panic(err)
+	}
+	if err := ValidateBatchID(id, false); err != nil {
+		panic(err)
+	}
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	iid := instanceID{scriptID: scriptID(sid), instanceID: id}
+	if v, found := s.instancesOptions[iid]; found {
+		return v.Get(s.b.buildCount)
+	}
+
+	fullID := "instance_" + s.key() + "_" + iid.String()
+
+	s.instancesOptions[iid] = newOpts[instanceID, paramsOptions](
+		iid,
+		fullID,
+		defaultOptionValues{},
+	)
+
+	return s.instancesOptions[iid].Get(s.b.buildCount)
+}
+
+func (g *scriptGroup) Reset() {
+	for _, v := range g.scriptsOptions {
+		v.Reset()
+	}
+	for _, v := range g.instancesOptions {
+		v.Reset()
+	}
+	for _, v := range g.runnersOptions {
+		v.Reset()
+	}
+}
+
+func (s *scriptGroup) Runner(id string) OptionsSetter {
+	if err := ValidateBatchID(id, false); err != nil {
+		panic(err)
+	}
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	sid := scriptID(id)
+	if v, found := s.runnersOptions[sid]; found {
+		return v.Get(s.b.buildCount)
+	}
+
+	runnerIdentity := "runner_" + s.key() + "_" + id
+
+	// A typical signature for a runner would be:
+	//     export default function Run(scripts) {}
+	// The user can override the default export in the templates.
+
+	s.runnersOptions[sid] = newOpts[scriptID, scriptOptions](
+		sid,
+		runnerIdentity,
+		defaultOptionValues{
+			defaultExport: "default",
+		},
+	)
+
+	return s.runnersOptions[sid].Get(s.b.buildCount)
+}
+
+func (s *scriptGroup) Script(id string) OptionsSetter {
+	if err := ValidateBatchID(id, false); err != nil {
+		panic(err)
+	}
+
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	sid := scriptID(id)
+	if v, found := s.scriptsOptions[sid]; found {
+		return v.Get(s.b.buildCount)
+	}
+
+	scriptIdentity := "script_" + s.key() + "_" + id
+
+	s.scriptsOptions[sid] = newOpts[scriptID, scriptOptions](
+		sid,
+		scriptIdentity,
+		defaultOptionValues{
+			defaultExport: "*",
+		},
+	)
+
+	return s.scriptsOptions[sid].Get(s.b.buildCount)
+}
+
+func (s *scriptGroup) isStale() bool {
+	for _, v := range s.scriptsOptions {
+		if v.isStale() {
+			return true
+		}
+	}
+
+	for _, v := range s.instancesOptions {
+		if v.isStale() {
+			return true
+		}
+	}
+
+	for _, v := range s.runnersOptions {
+		if v.isStale() {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (v *scriptGroup) forEachIdentity(
+	f func(id identity.Identity) bool,
+) bool {
+	if f(v) {
+		return true
+	}
+	for _, vv := range v.instancesOptions {
+		if f(vv.GetIdentity()) {
+			return true
+		}
+	}
+
+	for _, vv := range v.scriptsOptions {
+		if f(vv.GetIdentity()) {
+			return true
+		}
+	}
+
+	for _, vv := range v.runnersOptions {
+		if f(vv.GetIdentity()) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (s *scriptGroup) key() string {
+	return s.b.id + "_" + s.id
+}
+
+func (g *scriptGroup) removeNotSet() bool {
+	currentBuildID := g.b.buildCount
+	if !g.isBuilt(currentBuildID) {
+		// This group was never accessed in this build.
+		return false
+	}
+	var removed bool
+
+	if g.instancesOptions.isBuilt(currentBuildID) {
+		// A new instance has been set in this group for this build.
+		// Remove any instance that has not been set in this build.
+		for k, v := range g.instancesOptions {
+			if v.isBuilt(currentBuildID) {
+				continue
+			}
+			delete(g.instancesOptions, k)
+			removed = true
+		}
+	}
+
+	if g.runnersOptions.isBuilt(currentBuildID) {
+		// A new runner has been set in this group for this build.
+		// Remove any runner that has not been set in this build.
+		for k, v := range g.runnersOptions {
+			if v.isBuilt(currentBuildID) {
+				continue
+			}
+			delete(g.runnersOptions, k)
+			removed = true
+		}
+	}
+
+	if g.scriptsOptions.isBuilt(currentBuildID) {
+		// A new script has been set in this group for this build.
+		// Remove any script that has not been set in this build.
+		for k, v := range g.scriptsOptions {
+			if v.isBuilt(currentBuildID) {
+				continue
+			}
+			delete(g.scriptsOptions, k)
+
+			// Also remove any instance with this ID.
+			for kk := range g.instancesOptions {
+				if kk.scriptID == k {
+					delete(g.instancesOptions, kk)
+				}
+			}
+			removed = true
+		}
+	}
+
+	return removed
+}
+
+func (g *scriptGroup) removeTouchedButNotSet() bool {
+	currentBuildID := g.b.buildCount
+	var removed bool
+	for k, v := range g.instancesOptions {
+		if v.isBuilt(currentBuildID) {
+			continue
+		}
+		if v.isTouched(currentBuildID) {
+			delete(g.instancesOptions, k)
+			removed = true
+		}
+	}
+	for k, v := range g.runnersOptions {
+		if v.isBuilt(currentBuildID) {
+			continue
+		}
+		if v.isTouched(currentBuildID) {
+			delete(g.runnersOptions, k)
+			removed = true
+		}
+	}
+	for k, v := range g.scriptsOptions {
+		if v.isBuilt(currentBuildID) {
+			continue
+		}
+		if v.isTouched(currentBuildID) {
+			delete(g.scriptsOptions, k)
+			removed = true
+
+			// Also remove any instance with this ID.
+			for kk := range g.instancesOptions {
+				if kk.scriptID == k {
+					delete(g.instancesOptions, kk)
+				}
+			}
+		}
+
+	}
+	return removed
+}
+
+type scriptGroups map[string]*scriptGroup
+
+func (s scriptGroups) Sorted() []*scriptGroup {
+	var a []*scriptGroup
+	for _, v := range s {
+		a = append(a, v)
+	}
+	sort.Slice(a, func(i, j int) bool {
+		return a[i].id < a[j].id
+	})
+	return a
+}
+
+type scriptID string
+
+func (s scriptID) String() string {
+	return string(s)
+}
+
+type scriptInstanceBatchTemplateContext struct {
+	opts optionsGetSetter[instanceID, paramsOptions]
+}
+
+func (c scriptInstanceBatchTemplateContext) ID() string {
+	return c.opts.Key().instanceID
+}
+
+func (c scriptInstanceBatchTemplateContext) MarshalJSON() (b []byte, err error) {
+	return json.Marshal(&struct {
+		ID     string          `json:"id"`
+		Params json.RawMessage `json:"params"`
+	}{
+		ID:     c.opts.Key().instanceID,
+		Params: c.opts.Compiled().Params,
+	})
+}
+
+type scriptOptions struct {
+	// The script to build.
+	Resource resource.Resource
+
+	// The import context to use.
+	// Note that we will always fall back to the resource's own import context.
+	ImportContext resource.ResourceGetter
+
+	// The export name to use for this script's group's runners (if any).
+	// If not set, the default export will be used.
+	Export string
+
+	// Params marshaled to JSON.
+	Params json.RawMessage
+}
+
+func (o *scriptOptions) Dir() string {
+	return path.Dir(resources.InternalResourceTargetPath(o.Resource))
+}
+
+func (s scriptOptions) IsZero() bool {
+	return s.Resource == nil
+}
+
+func (s scriptOptions) isStaleCompiled(prev scriptOptions) bool {
+	if prev.IsZero() {
+		return false
+	}
+
+	// All but the ImportContext are checked at the options/map level.
+	i1nil, i2nil := prev.ImportContext == nil, s.ImportContext == nil
+	if i1nil && i2nil {
+		return false
+	}
+	if i1nil || i2nil {
+		return true
+	}
+	// On its own this check would have too many false positives, but combined with the other checks it should be fine.
+	// We cannot do equality checking here.
+	if !prev.ImportContext.(resource.IsProbablySameResourceGetter).IsProbablySameResourceGetter(s.ImportContext) {
+		return true
+	}
+
+	return false
+}
+
+func (s scriptOptions) compileOptions(m map[string]any, defaults defaultOptionValues) (scriptOptions, error) {
+	v := struct {
+		Resource      resource.Resource
+		ImportContext any
+		Export        string
+		Params        map[string]any
+	}{}
+
+	if err := mapstructure.WeakDecode(m, &v); err != nil {
+		panic(err)
+	}
+
+	var paramsJSON []byte
+	if v.Params != nil {
+		var err error
+		paramsJSON, err = json.Marshal(v.Params)
+		if err != nil {
+			panic(err)
+		}
+	}
+
+	if v.Export == "" {
+		v.Export = defaults.defaultExport
+	}
+
+	compiled := scriptOptions{
+		Resource:      v.Resource,
+		Export:        v.Export,
+		ImportContext: resource.NewCachedResourceGetter(v.ImportContext),
+		Params:        paramsJSON,
+	}
+
+	if compiled.Resource == nil {
+		return scriptOptions{}, fmt.Errorf("resource not set")
+	}
+
+	return compiled, nil
+}
+
+type scriptRunnerTemplateContext struct {
+	opts   optionsGetSetter[scriptID, scriptOptions]
+	Import string
+}
+
+func (s *scriptRunnerTemplateContext) Export() string {
+	return s.opts.Compiled().Export
+}
+
+func (c scriptRunnerTemplateContext) MarshalJSON() (b []byte, err error) {
+	return json.Marshal(&struct {
+		ID string `json:"id"`
+	}{
+		ID: c.opts.Key().String(),
+	})
+}
+
+func (o optionsMap[K, C]) isBuilt(id uint32) bool {
+	for _, v := range o {
+		if v.isBuilt(id) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (o *opts[K, C]) isBuilt(id uint32) bool {
+	return o.h.isBuilt(id)
+}
+
+func (o *opts[K, C]) isStale() bool {
+	if o.h.isStaleOpts() {
+		return true
+	}
+	if o.h.compiled.isStaleCompiled(o.h.compiledPrev) {
+		return true
+	}
+	return false
+}
+
+func (o *optsHolder[C]) isStaleOpts() bool {
+	if o.optsSetCounter == 1 && o.resetCounter > 0 {
+		return false
+	}
+	isStale := func() bool {
+		if len(o.optsCurr) != len(o.optsPrev) {
+			return true
+		}
+		for k, v := range o.optsPrev {
+			vv, found := o.optsCurr[k]
+			if !found {
+				return true
+			}
+			if strings.EqualFold(k, propsKeyImportContext) {
+				// This is checked later.
+			} else if si, ok := vv.(resource.StaleInfo); ok {
+				if si.StaleVersion() > 0 {
+					return true
+				}
+			} else {
+				if !reflect.DeepEqual(v, vv) {
+					return true
+				}
+			}
+		}
+		return false
+	}()
+
+	return isStale
+}
+
+func (o *opts[K, C]) isTouched(id uint32) bool {
+	return o.h.isTouched(id)
+}
+
+func (o *optsHolder[C]) checkCompileErr() {
+	if o.compileErr != nil {
+		panic(o.compileErr)
+	}
+}
+
+func (o *opts[K, C]) currPrev() (map[string]any, map[string]any) {
+	return o.h.optsCurr, o.h.optsPrev
+}
+
+func init() {
+	// We don't want any dependencies/change tracking on the top level Package,
+	// we want finer grained control via Package.Group.
+	var p any = &Package{}
+	if _, ok := p.(identity.Identity); ok {
+		panic("esbuid.Package should not implement identity.Identity")
+	}
+	if _, ok := p.(identity.DependencyManagerProvider); ok {
+		panic("esbuid.Package should not implement identity.DependencyManagerProvider")
+	}
+}
diff --git a/internal/js/esbuild/batch_integration_test.go b/internal/js/esbuild/batch_integration_test.go
new file mode 100644
index 000000000..07f99ee4e
--- /dev/null
+++ b/internal/js/esbuild/batch_integration_test.go
@@ -0,0 +1,686 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package js provides functions for building JavaScript resources
+package esbuild_test
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+
+	"github.com/bep/logg"
+	"github.com/gohugoio/hugo/common/paths"
+	"github.com/gohugoio/hugo/hugolib"
+	"github.com/gohugoio/hugo/internal/js/esbuild"
+)
+
+// Used to test misc. error situations etc.
+const jsBatchFilesTemplate = `
+-- hugo.toml --
+disableKinds = ["taxonomy", "term", "section"]
+disableLiveReload = true
+-- assets/js/styles.css --
+body {
+	background-color: red;
+}
+-- assets/js/main.js --
+import './styles.css';
+import * as params from '@params';
+import * as foo from 'mylib';
+console.log("Hello, Main!");
+console.log("params.p1", params.p1);
+export default function Main() {};
+-- assets/js/runner.js --
+console.log("Hello, Runner!");
+-- node_modules/mylib/index.js --
+console.log("Hello, My Lib!");
+-- layouts/shortcodes/hdx.html --
+{{ $path := .Get "r" }}
+{{ $r := or (.Page.Resources.Get $path) (resources.Get $path) }}
+{{ $batch := (js.Batch "mybatch") }}
+{{ $scriptID := $path | anchorize }}
+{{ $instanceID :=  .Ordinal | string }}
+{{ $group := .Page.RelPermalink | anchorize }}
+{{ $params := .Params | default dict }}
+{{ $export := .Get "export" | default "default" }}
+{{ with $batch.Group $group }}
+	{{ with .Runner "create-elements" }}
+		{{ .SetOptions (dict "resource" (resources.Get "js/runner.js")) }}
+	{{ end }}
+	{{ with .Script $scriptID }}
+		{{ .SetOptions (dict
+			"resource" $r
+			"export" $export
+			"importContext" (slice $.Page)
+		)
+		}}
+		{{ end }}
+	{{ with .Instance $scriptID $instanceID }}
+		{{ .SetOptions (dict "params" $params) }}
+	{{ end }}
+{{ end }}
+hdx-instance: {{ $scriptID }}: {{ $instanceID }}|
+-- layouts/_default/baseof.html --
+Base.
+{{ $batch := (js.Batch "mybatch") }}
+ {{ with $batch.Config }}
+	{{ .SetOptions (dict 
+		"params" (dict "id" "config")
+		"sourceMap" ""
+		)
+	}}
+{{ end }}
+{{ with (templates.Defer (dict "key" "global")) }}
+Defer:
+{{ $batch := (js.Batch "mybatch") }}
+{{ range $k, $v := $batch.Build.Groups }}
+	{{ range $kk, $vv := . -}}
+		{{ $k }}: {{ .RelPermalink }}
+	{{ end }}
+{{ end -}}
+{{ end }}
+{{ block "main" . }}Main{{ end }}
+End.
+-- layouts/_default/single.html --
+{{ define "main" }}
+==> Single Template Content: {{ .Content }}$
+{{ $batch := (js.Batch "mybatch") }}
+{{ with $batch.Group "mygroup" }}
+ 	{{ with .Runner "run" }}
+		{{ .SetOptions (dict "resource" (resources.Get "js/runner.js")) }}
+	{{ end }}
+	{{ with .Script "main" }}
+		{{ .SetOptions (dict "resource" (resources.Get "js/main.js") "params" (dict "p1" "param-p1-main" )) }}
+	{{ end }}
+	{{ with .Instance "main" "i1" }}
+		{{ .SetOptions (dict "params" (dict "title" "Instance 1")) }}
+	{{ end }}
+{{ end }}
+{{ end }}
+-- layouts/index.html --
+{{ define "main" }}
+Home.
+{{ end }}
+-- content/p1/index.md --
+---
+title: "P1"
+---
+
+Some content.
+
+{{< hdx r="p1script.js" myparam="p1-param-1" >}}
+{{< hdx r="p1script.js" myparam="p1-param-2" >}}
+
+-- content/p1/p1script.js --
+console.log("P1 Script");
+
+
+`
+
+// Just to verify that the above file setup works.
+func TestBatchTemplateOKBuild(t *testing.T) {
+	b := hugolib.Test(t, jsBatchFilesTemplate, hugolib.TestOptWithOSFs())
+	b.AssertPublishDir("mybatch/mygroup.js", "mybatch/mygroup.css")
+}
+
+func TestBatchRemoveAllInGroup(t *testing.T) {
+	files := jsBatchFilesTemplate
+	b := hugolib.TestRunning(t, files, hugolib.TestOptWithOSFs())
+
+	b.AssertFileContent("public/p1/index.html", "p1: /mybatch/p1.js")
+
+	b.EditFiles("content/p1/index.md", `
+---
+title: "P1"
+---
+Empty.
+`)
+	b.Build()
+
+	b.AssertFileContent("public/p1/index.html", "! p1: /mybatch/p1.js")
+
+	// Add one script back.
+	b.EditFiles("content/p1/index.md", `
+---
+title: "P1"
+---
+
+{{< hdx r="p1script.js" myparam="p1-param-1-new" >}}
+`)
+	b.Build()
+
+	b.AssertFileContent("public/mybatch/p1.js",
+		"p1-param-1-new",
+		"p1script.js")
+}
+
+func TestBatchEditInstance(t *testing.T) {
+	files := jsBatchFilesTemplate
+	b := hugolib.TestRunning(t, files, hugolib.TestOptWithOSFs())
+	b.AssertFileContent("public/mybatch/mygroup.js", "Instance 1")
+	b.EditFileReplaceAll("layouts/_default/single.html", "Instance 1", "Instance 1 Edit").Build()
+	b.AssertFileContent("public/mybatch/mygroup.js", "Instance 1 Edit")
+}
+
+func TestBatchEditScriptParam(t *testing.T) {
+	files := jsBatchFilesTemplate
+	b := hugolib.TestRunning(t, files, hugolib.TestOptWithOSFs())
+	b.AssertFileContent("public/mybatch/mygroup.js", "param-p1-main")
+	b.EditFileReplaceAll("layouts/_default/single.html", "param-p1-main", "param-p1-main-edited").Build()
+	b.AssertFileContent("public/mybatch/mygroup.js", "param-p1-main-edited")
+}
+
+func TestBatchErrorScriptResourceNotSet(t *testing.T) {
+	files := strings.Replace(jsBatchFilesTemplate, `(resources.Get "js/main.js")`, `(resources.Get "js/doesnotexist.js")`, 1)
+	b, err := hugolib.TestE(t, files, hugolib.TestOptWithOSFs())
+	b.Assert(err, qt.IsNotNil)
+	b.Assert(err.Error(), qt.Contains, `error calling SetOptions: resource not set`)
+}
+
+func TestBatchSlashInBatchID(t *testing.T) {
+	files := strings.ReplaceAll(jsBatchFilesTemplate, `"mybatch"`, `"my/batch"`)
+	b, err := hugolib.TestE(t, files, hugolib.TestOptWithOSFs())
+	b.Assert(err, qt.IsNil)
+	b.AssertPublishDir("my/batch/mygroup.js")
+}
+
+func TestBatchSourceMaps(t *testing.T) {
+	filesTemplate := `
+-- hugo.toml --
+disableKinds = ["taxonomy", "term", "section"]
+disableLiveReload = true
+-- assets/js/styles.css --
+body {
+	background-color: red;
+}
+-- assets/js/main.js --
+import * as foo from 'mylib';
+console.log("Hello, Main!");
+-- assets/js/runner.js --
+console.log("Hello, Runner!");
+-- node_modules/mylib/index.js --
+console.log("Hello, My Lib!");
+-- layouts/shortcodes/hdx.html --
+{{ $path := .Get "r" }}
+{{ $r := or (.Page.Resources.Get $path) (resources.Get $path) }}
+{{ $batch := (js.Batch "mybatch") }}
+{{ $scriptID := $path | anchorize }}
+{{ $instanceID :=  .Ordinal | string }}
+{{ $group := .Page.RelPermalink | anchorize }}
+{{ $params := .Params | default dict }}
+{{ $export := .Get "export" | default "default" }}
+{{ with $batch.Group $group }}
+	{{ with .Runner "create-elements" }}
+		{{ .SetOptions (dict "resource" (resources.Get "js/runner.js")) }}
+	{{ end }}
+	{{ with .Script $scriptID }}
+		{{ .SetOptions (dict
+			"resource" $r
+			"export" $export
+			"importContext" (slice $.Page)
+		)
+		}}
+		{{ end }}
+	{{ with .Instance $scriptID $instanceID }}
+		{{ .SetOptions (dict "params" $params) }}
+	{{ end }}
+{{ end }}
+hdx-instance: {{ $scriptID }}: {{ $instanceID }}|
+-- layouts/_default/baseof.html --
+Base.
+{{ $batch := (js.Batch "mybatch") }}
+ {{ with $batch.Config }}
+	{{ .SetOptions (dict 
+		"params" (dict "id" "config")
+		"sourceMap" ""
+		)
+	}}
+{{ end }}
+{{ with (templates.Defer (dict "key" "global")) }}
+Defer:
+{{ $batch := (js.Batch "mybatch") }}
+{{ range $k, $v := $batch.Build.Groups }}
+	{{ range $kk, $vv := . -}}
+		{{ $k }}: {{ .RelPermalink }}
+	{{ end }}
+{{ end -}}
+{{ end }}
+{{ block "main" . }}Main{{ end }}
+End.
+-- layouts/_default/single.html --
+{{ define "main" }}
+==> Single Template Content: {{ .Content }}$
+{{ $batch := (js.Batch "mybatch") }}
+{{ with $batch.Group "mygroup" }}
+ 	{{ with .Runner "run" }}
+		{{ .SetOptions (dict "resource" (resources.Get "js/runner.js")) }}
+	{{ end }}
+	{{ with .Script "main" }}
+		{{ .SetOptions (dict "resource" (resources.Get "js/main.js") "params" (dict "p1" "param-p1-main" )) }}
+	{{ end }}
+	{{ with .Instance "main" "i1" }}
+		{{ .SetOptions (dict "params" (dict "title" "Instance 1")) }}
+	{{ end }}
+{{ end }}
+{{ end }}
+-- layouts/index.html --
+{{ define "main" }}
+Home.
+{{ end }}
+-- content/p1/index.md --
+---
+title: "P1"
+---
+
+Some content.
+
+{{< hdx r="p1script.js" myparam="p1-param-1" >}}
+{{< hdx r="p1script.js" myparam="p1-param-2" >}}
+
+-- content/p1/p1script.js --
+import * as foo from 'mylib';
+console.lg("Foo", foo);
+console.log("P1 Script");
+export default function P1Script() {};
+
+
+`
+	files := strings.Replace(filesTemplate, `"sourceMap" ""`, `"sourceMap" "linked"`, 1)
+	b := hugolib.TestRunning(t, files, hugolib.TestOptWithOSFs())
+	b.AssertFileContent("public/mybatch/mygroup.js.map", "main.js", "! ns-hugo")
+	b.AssertFileContent("public/mybatch/mygroup.js", "sourceMappingURL=mygroup.js.map")
+	b.AssertFileContent("public/mybatch/p1.js", "sourceMappingURL=p1.js.map")
+	b.AssertFileContent("public/mybatch/mygroup_run_runner.js", "sourceMappingURL=mygroup_run_runner.js.map")
+	b.AssertFileContent("public/mybatch/chunk-UQKPPNA6.js", "sourceMappingURL=chunk-UQKPPNA6.js.map")
+
+	checkMap := func(p string, expectLen int) {
+		s := b.FileContent(p)
+		sources := esbuild.SourcesFromSourceMap(s)
+		b.Assert(sources, qt.HasLen, expectLen)
+
+		// Check that all source files exist.
+		for _, src := range sources {
+			filename, ok := paths.UrlStringToFilename(src)
+			b.Assert(ok, qt.IsTrue)
+			_, err := os.Stat(filename)
+			b.Assert(err, qt.IsNil)
+		}
+	}
+
+	checkMap("public/mybatch/mygroup.js.map", 1)
+	checkMap("public/mybatch/p1.js.map", 1)
+	checkMap("public/mybatch/mygroup_run_runner.js.map", 0)
+	checkMap("public/mybatch/chunk-UQKPPNA6.js.map", 1)
+}
+
+func TestBatchErrorRunnerResourceNotSet(t *testing.T) {
+	files := strings.Replace(jsBatchFilesTemplate, `(resources.Get "js/runner.js")`, `(resources.Get "js/doesnotexist.js")`, 1)
+	b, err := hugolib.TestE(t, files, hugolib.TestOptWithOSFs())
+	b.Assert(err, qt.IsNotNil)
+	b.Assert(err.Error(), qt.Contains, `resource not set`)
+}
+
+func TestBatchErrorScriptResourceInAssetsSyntaxError(t *testing.T) {
+	// Introduce JS syntax error in assets/js/main.js
+	files := strings.Replace(jsBatchFilesTemplate, `console.log("Hello, Main!");`, `console.log("Hello, Main!"`, 1)
+	b, err := hugolib.TestE(t, files, hugolib.TestOptWithOSFs())
+	b.Assert(err, qt.IsNotNil)
+	b.Assert(err.Error(), qt.Contains, filepath.FromSlash(`assets/js/main.js:5:0": Expected ")" but found "console"`))
+}
+
+func TestBatchErrorScriptResourceInBundleSyntaxError(t *testing.T) {
+	// Introduce JS syntax error in content/p1/p1script.js
+	files := strings.Replace(jsBatchFilesTemplate, `console.log("P1 Script");`, `console.log("P1 Script"`, 1)
+	b, err := hugolib.TestE(t, files, hugolib.TestOptWithOSFs())
+	b.Assert(err, qt.IsNotNil)
+	b.Assert(err.Error(), qt.Contains, filepath.FromSlash(`/content/p1/p1script.js:3:0": Expected ")" but found end of file`))
+}
+
+func TestBatch(t *testing.T) {
+	files := `
+-- hugo.toml --
+disableKinds = ["taxonomy", "term"]
+disableLiveReload = true
+baseURL = "https://example.com"
+-- package.json --
+{
+  "devDependencies": {
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1"
+  }
+}
+-- assets/js/shims/react.js --
+-- assets/js/shims/react-dom.js --
+module.exports = window.ReactDOM;
+module.exports = window.React;
+-- content/mybundle/index.md --
+---
+title: "My Bundle"
+---
+-- content/mybundle/mybundlestyles.css --
+@import './foo.css';
+@import './bar.css';
+@import './otherbundlestyles.css';
+
+.mybundlestyles {
+	background-color: blue;
+}
+-- content/mybundle/bundlereact.jsx --
+import * as React from "react";
+import './foo.css';
+import './mybundlestyles.css';
+window.React1 = React;
+
+let text = 'Click me, too!'
+
+export default function MyBundleButton() {
+    return (
+        <button>${text}</button>
+    )
+}
+
+-- assets/js/reactrunner.js --
+import * as ReactDOM from 'react-dom/client';
+import * as React from 'react';
+
+export default function Run(group) {
+	for (const module of group.scripts) {
+		for (const instance of module.instances) {
+			/* This is a convention in this project. */
+			let elId = §§${module.id}-${instance.id}§§;
+			let el = document.getElementById(elId);
+			if (!el) {
+				console.warn(§§Element with id ${elId} not found§§);
+				continue;
+			}
+			const root = ReactDOM.createRoot(el);
+			const reactEl = React.createElement(module.mod, instance.params);
+			root.render(reactEl);
+		}
+	}
+}
+-- assets/other/otherbundlestyles.css --
+.otherbundlestyles {
+	background-color: red;
+}
+-- assets/other/foo.css --
+@import './bar.css';
+
+.foo {
+	background-color: blue;
+}
+-- assets/other/bar.css --
+.bar {
+	background-color: red;
+}
+-- assets/js/button.css --
+button {
+	background-color: red;
+}
+-- assets/js/bar.css --
+.bar-assets {
+	background-color: red;
+}
+-- assets/js/helper.js --
+import './bar.css'
+
+export function helper() {
+	console.log('helper');
+}	
+
+-- assets/js/react1styles_nested.css --
+.react1styles_nested {
+	background-color: red;
+}
+-- assets/js/react1styles.css --
+@import './react1styles_nested.css';
+.react1styles {
+	background-color: red;
+}
+-- assets/js/react1.jsx --
+import * as React from "react";
+import './button.css'
+import './foo.css'
+import './react1styles.css'
+
+window.React1 = React;
+
+let text = 'Click me'
+
+export default function MyButton() {
+    return (
+        <button>${text}</button>
+    )
+}
+	
+-- assets/js/react2.jsx --
+import * as React from "react";
+import { helper } from './helper.js'
+import './foo.css'
+
+window.React2 = React;
+
+let text = 'Click me, too!'
+
+export function MyOtherButton() {
+    return (
+        <button>${text}</button>
+    )
+}
+-- assets/js/main1.js --
+import * as React from "react";
+import * as params from '@params';
+
+console.log('main1.React', React)
+console.log('main1.params.id', params.id)
+
+-- assets/js/main2.js --
+import * as React from "react";
+import * as params from '@params';
+
+console.log('main2.React', React)
+console.log('main2.params.id', params.id)
+
+export default function Main2() {};
+
+-- assets/js/main3.js --
+import * as React from "react";
+import * as params from '@params';
+import * as config from '@params/config';
+
+console.log('main3.params.id', params.id)
+console.log('config.params.id', config.id)
+
+export default function Main3() {};
+
+-- layouts/_default/single.html --
+Single.
+
+{{ $r := .Resources.GetMatch "*.jsx" }}
+{{ $batch := (js.Batch "mybundle") }}
+{{ $otherCSS := (resources.Match "/other/*.css").Mount "/other" "." }}
+ {{ with $batch.Config }}
+	  {{ $shims := dict "react" "js/shims/react.js"  "react-dom/client" "js/shims/react-dom.js" }}
+      {{ .SetOptions (dict 
+           "target" "es2018"
+           "params" (dict "id" "config")
+		   "shims" $shims
+	     )
+      }}
+{{ end }}
+{{ with $batch.Group "reactbatch" }}
+	{{ with .Script "r3" }}
+		 	{{ .SetOptions (dict
+			 	"resource" $r
+ 				"importContext" (slice $ $otherCSS)
+				"params" (dict "id" "r3")
+               )
+			}}
+	{{ end }}
+	{{ with .Instance "r3" "r2i1" }}
+	 	{{ .SetOptions  (dict "title" "r2 instance 1")}}
+	{{ end }}
+{{ end }}
+-- layouts/index.html --
+Home.
+{{ with (templates.Defer (dict "key" "global")) }}
+{{ $batch := (js.Batch "mybundle") }}
+{{ range $k, $v := $batch.Build.Groups }}
+ {{ range $kk, $vv := . }}
+	 {{ $k }}: {{ $kk }}: {{ .RelPermalink }}
+  {{ end }}
+ {{ end }}
+{{ end }}
+{{ $myContentBundle := site.GetPage "mybundle" }}
+{{ $batch := (js.Batch "mybundle") }}
+{{ $otherCSS := (resources.Match "/other/*.css").Mount "/other" "." }}
+{{ with $batch.Group "mains" }}
+  {{ with .Script "main1" }}
+	{{ .SetOptions (dict
+			 	"resource" (resources.Get "js/main1.js")
+				"params" (dict "id" "main1")
+            )
+	}}
+  {{ end }}
+  {{ with .Script "main2" }}
+   {{ .SetOptions (dict
+			 	"resource" (resources.Get "js/main2.js")
+				"params" (dict "id" "main2")
+            )
+  }}
+  {{ end }}
+ {{ with .Script "main3" }}
+   {{ .SetOptions (dict
+			 	"resource" (resources.Get "js/main3.js")
+            )
+  }}
+  {{ end }}
+{{ with .Instance "main1" "m1i1" }}{{ .SetOptions (dict "params" (dict "title" "Main1 Instance 1"))}}{{ end }}
+{{ with .Instance "main1" "m1i2" }}{{ .SetOptions (dict "params" (dict "title" "Main1 Instance 2"))}}{{ end }}
+{{ end }}
+{{ with $batch.Group "reactbatch" }}
+ 	{{ with .Runner "reactrunner" }}
+		{{ .SetOptions ( dict "resource"  (resources.Get "js/reactrunner.js") )}}
+	{{ end }}
+	{{ with .Script "r1" }}
+		{{ .SetOptions (dict
+			"resource" (resources.Get "js/react1.jsx")
+			"importContext" (slice $myContentBundle $otherCSS)
+			"params" (dict "id" "r1")
+			)
+		}}
+	{{ end }}
+	{{ with .Instance "r1" "i1" }}{{ .SetOptions (dict "params" (dict "title" "Instance 1"))}}{{ end }}
+	{{ with .Instance "r1" "i2" }}{{ .SetOptions (dict "params" (dict "title" "Instance 2"))}}{{ end }}
+	{{ with .Script "r2" }}
+		{{ .SetOptions (dict
+			"resource" (resources.Get "js/react2.jsx")
+			"export" "MyOtherButton"
+			"importContext" $otherCSS
+			"params" (dict "id" "r2")
+			)
+		}}
+	{{ end }}
+	{{ with .Instance "r2" "i1" }}{{ .SetOptions (dict "params" (dict "title" "Instance 2-1"))}}{{ end }}
+{{ end }}
+ 
+`
+
+	b := hugolib.NewIntegrationTestBuilder(
+		hugolib.IntegrationTestConfig{
+			T:               t,
+			NeedsOsFS:       true,
+			NeedsNpmInstall: true,
+			TxtarString:     files,
+			Running:         true,
+			LogLevel:        logg.LevelWarn,
+			// PrintAndKeepTempDir: true,
+		}).Build()
+
+	b.AssertFileContent("public/index.html",
+		"mains: 0: /mybundle/mains.js",
+		"reactbatch: 2: /mybundle/reactbatch.css",
+	)
+
+	b.AssertFileContent("public/mybundle/reactbatch.css",
+		".bar {",
+	)
+
+	// Verify params resolution.
+	b.AssertFileContent("public/mybundle/mains.js",
+		`
+var id = "main1";
+console.log("main1.params.id", id);
+var id2 = "main2";
+console.log("main2.params.id", id2);
+
+
+# Params from top level config.
+var id3 = "config";
+console.log("main3.params.id", void 0);
+console.log("config.params.id", id3);
+`)
+
+	b.EditFileReplaceAll("content/mybundle/mybundlestyles.css", ".mybundlestyles", ".mybundlestyles-edit").Build()
+	b.AssertFileContent("public/mybundle/reactbatch.css", ".mybundlestyles-edit {")
+
+	b.EditFileReplaceAll("assets/other/bar.css", ".bar {", ".bar-edit {").Build()
+	b.AssertFileContent("public/mybundle/reactbatch.css", ".bar-edit {")
+
+	b.EditFileReplaceAll("assets/other/bar.css", ".bar-edit {", ".bar-edit2 {").Build()
+	b.AssertFileContent("public/mybundle/reactbatch.css", ".bar-edit2 {")
+}
+
+func TestEditBaseofManyTimes(t *testing.T) {
+	files := `
+-- hugo.toml --
+baseURL = "https://example.com"
+disableLiveReload = true
+disableKinds = ["taxonomy", "term"]
+-- layouts/_default/baseof.html --
+Baseof.
+{{ block "main" . }}{{ end }}
+{{ with (templates.Defer (dict "key" "global")) }}
+Now. {{ now }}
+{{ end }}
+-- layouts/_default/single.html --
+{{ define "main" }}
+Single.
+{{ end }}
+--
+-- layouts/_default/list.html --
+{{ define "main" }}
+List.
+{{ end }}
+-- content/mybundle/index.md --
+---
+title: "My Bundle"
+---
+-- content/_index.md --
+---
+title: "Home"
+---
+`
+
+	b := hugolib.TestRunning(t, files)
+	b.AssertFileContent("public/index.html", "Baseof.")
+
+	for i := 0; i < 100; i++ {
+		b.EditFileReplaceAll("layouts/_default/baseof.html", "Now", "Now.").Build()
+		b.AssertFileContent("public/index.html", "Now..")
+	}
+}
diff --git a/internal/js/esbuild/build.go b/internal/js/esbuild/build.go
new file mode 100644
index 000000000..33b91eafc
--- /dev/null
+++ b/internal/js/esbuild/build.go
@@ -0,0 +1,236 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package esbuild provides functions for building JavaScript resources.
+package esbuild
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/evanw/esbuild/pkg/api"
+	"github.com/gohugoio/hugo/common/herrors"
+	"github.com/gohugoio/hugo/common/hugio"
+	"github.com/gohugoio/hugo/common/text"
+	"github.com/gohugoio/hugo/hugofs"
+	"github.com/gohugoio/hugo/hugolib/filesystems"
+	"github.com/gohugoio/hugo/identity"
+	"github.com/gohugoio/hugo/resources"
+)
+
+// NewBuildClient creates a new BuildClient.
+func NewBuildClient(fs *filesystems.SourceFilesystem, rs *resources.Spec) *BuildClient {
+	return &BuildClient{
+		rs:  rs,
+		sfs: fs,
+	}
+}
+
+// BuildClient is a client for building JavaScript resources using esbuild.
+type BuildClient struct {
+	rs  *resources.Spec
+	sfs *filesystems.SourceFilesystem
+}
+
+// Build builds the given JavaScript resources using esbuild with the given options.
+func (c *BuildClient) Build(opts Options) (api.BuildResult, error) {
+	dependencyManager := opts.DependencyManager
+	if dependencyManager == nil {
+		dependencyManager = identity.NopManager
+	}
+
+	opts.OutDir = c.rs.AbsPublishDir
+	opts.ResolveDir = c.rs.Cfg.BaseConfig().WorkingDir // where node_modules gets resolved
+	opts.AbsWorkingDir = opts.ResolveDir
+	opts.TsConfig = c.rs.ResolveJSConfigFile("tsconfig.json")
+	assetsResolver := newFSResolver(c.rs.Assets.Fs)
+
+	if err := opts.validate(); err != nil {
+		return api.BuildResult{}, err
+	}
+
+	if err := opts.compile(); err != nil {
+		return api.BuildResult{}, err
+	}
+
+	var err error
+	opts.compiled.Plugins, err = createBuildPlugins(c.rs, assetsResolver, dependencyManager, opts)
+	if err != nil {
+		return api.BuildResult{}, err
+	}
+
+	if opts.Inject != nil {
+		// Resolve the absolute filenames.
+		for i, ext := range opts.Inject {
+			impPath := filepath.FromSlash(ext)
+			if filepath.IsAbs(impPath) {
+				return api.BuildResult{}, fmt.Errorf("inject: absolute paths not supported, must be relative to /assets")
+			}
+
+			m := assetsResolver.resolveComponent(impPath)
+
+			if m == nil {
+				return api.BuildResult{}, fmt.Errorf("inject: file %q not found", ext)
+			}
+
+			opts.Inject[i] = m.Filename
+
+		}
+
+		opts.compiled.Inject = opts.Inject
+
+	}
+
+	result := api.Build(opts.compiled)
+
+	if len(result.Errors) > 0 {
+		createErr := func(msg api.Message) error {
+			if msg.Location == nil {
+				return errors.New(msg.Text)
+			}
+			var (
+				contentr     hugio.ReadSeekCloser
+				errorMessage string
+				loc          = msg.Location
+				errorPath    = loc.File
+				err          error
+			)
+
+			var resolvedError *ErrorMessageResolved
+
+			if opts.ErrorMessageResolveFunc != nil {
+				resolvedError = opts.ErrorMessageResolveFunc(msg)
+			}
+
+			if resolvedError == nil {
+				if errorPath == stdinImporter {
+					errorPath = opts.StdinSourcePath
+				}
+
+				errorMessage = msg.Text
+
+				var namespace string
+				for _, ns := range hugoNamespaces {
+					if strings.HasPrefix(errorPath, ns) {
+						namespace = ns
+						break
+					}
+				}
+
+				if namespace != "" {
+					namespace += ":"
+					errorMessage = strings.ReplaceAll(errorMessage, namespace, "")
+					errorPath = strings.TrimPrefix(errorPath, namespace)
+					contentr, err = hugofs.Os.Open(errorPath)
+				} else {
+					var fi os.FileInfo
+					fi, err = c.sfs.Fs.Stat(errorPath)
+					if err == nil {
+						m := fi.(hugofs.FileMetaInfo).Meta()
+						errorPath = m.Filename
+						contentr, err = m.Open()
+					}
+				}
+			} else {
+				contentr = resolvedError.Content
+				errorPath = resolvedError.Path
+				errorMessage = resolvedError.Message
+			}
+
+			if contentr != nil {
+				defer contentr.Close()
+			}
+
+			if err == nil {
+				fe := herrors.
+					NewFileErrorFromName(errors.New(errorMessage), errorPath).
+					UpdatePosition(text.Position{Offset: -1, LineNumber: loc.Line, ColumnNumber: loc.Column}).
+					UpdateContent(contentr, nil)
+
+				return fe
+			}
+
+			return fmt.Errorf("%s", errorMessage)
+		}
+
+		var errors []error
+
+		for _, msg := range result.Errors {
+			errors = append(errors, createErr(msg))
+		}
+
+		// Return 1, log the rest.
+		for i, err := range errors {
+			if i > 0 {
+				c.rs.Logger.Errorf("js.Build failed: %s", err)
+			}
+		}
+
+		return result, errors[0]
+	}
+
+	inOutputPathToAbsFilename := opts.ResolveSourceMapSource
+	opts.ResolveSourceMapSource = func(s string) string {
+		if inOutputPathToAbsFilename != nil {
+			if filename := inOutputPathToAbsFilename(s); filename != "" {
+				return filename
+			}
+		}
+
+		if m := assetsResolver.resolveComponent(s); m != nil {
+			return m.Filename
+		}
+
+		return ""
+	}
+
+	for i, o := range result.OutputFiles {
+		if err := fixOutputFile(&o, func(s string) string {
+			if s == "<stdin>" {
+				return opts.ResolveSourceMapSource(opts.StdinSourcePath)
+			}
+			var isNsHugo bool
+			if strings.HasPrefix(s, "ns-hugo") {
+				isNsHugo = true
+				idxColon := strings.Index(s, ":")
+				s = s[idxColon+1:]
+			}
+
+			if !strings.HasPrefix(s, PrefixHugoVirtual) {
+				if !filepath.IsAbs(s) {
+					s = filepath.Join(opts.OutDir, s)
+				}
+			}
+
+			if isNsHugo {
+				if ss := opts.ResolveSourceMapSource(s); ss != "" {
+					if strings.HasPrefix(ss, PrefixHugoMemory) {
+						// File not on disk, mark it for removal from the sources slice.
+						return ""
+					}
+					return ss
+				}
+				return ""
+			}
+			return s
+		}); err != nil {
+			return result, err
+		}
+		result.OutputFiles[i] = o
+	}
+
+	return result, nil
+}
diff --git a/resources/resource_transformers/js/build_test.go b/internal/js/esbuild/helpers.go
index 30a4490ed..b4cb565b8 100644
--- a/resources/resource_transformers/js/build_test.go
+++ b/internal/js/esbuild/helpers.go
@@ -1,4 +1,4 @@
-// Copyright 2020 The Hugo Authors. All rights reserved.
+// Copyright 2024 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -11,4 +11,5 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package js
+// Package esbuild provides functions for building JavaScript resources.
+package esbuild
diff --git a/internal/js/esbuild/options.go b/internal/js/esbuild/options.go
new file mode 100644
index 000000000..16fc0d4bb
--- /dev/null
+++ b/internal/js/esbuild/options.go
@@ -0,0 +1,375 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package esbuild
+
+import (
+	"encoding/json"
+	"fmt"
+	"path/filepath"
+	"strings"
+
+	"github.com/gohugoio/hugo/common/hugio"
+	"github.com/gohugoio/hugo/common/maps"
+	"github.com/gohugoio/hugo/common/paths"
+	"github.com/gohugoio/hugo/identity"
+
+	"github.com/evanw/esbuild/pkg/api"
+
+	"github.com/gohugoio/hugo/media"
+	"github.com/mitchellh/mapstructure"
+)
+
+var (
+	nameTarget = map[string]api.Target{
+		"":       api.ESNext,
+		"esnext": api.ESNext,
+		"es5":    api.ES5,
+		"es6":    api.ES2015,
+		"es2015": api.ES2015,
+		"es2016": api.ES2016,
+		"es2017": api.ES2017,
+		"es2018": api.ES2018,
+		"es2019": api.ES2019,
+		"es2020": api.ES2020,
+		"es2021": api.ES2021,
+		"es2022": api.ES2022,
+		"es2023": api.ES2023,
+	}
+
+	// source names: https://github.com/evanw/esbuild/blob/9eca46464ed5615cb36a3beb3f7a7b9a8ffbe7cf/internal/config/config.go#L208
+	nameLoader = map[string]api.Loader{
+		"none":       api.LoaderNone,
+		"base64":     api.LoaderBase64,
+		"binary":     api.LoaderBinary,
+		"copy":       api.LoaderFile,
+		"css":        api.LoaderCSS,
+		"dataurl":    api.LoaderDataURL,
+		"default":    api.LoaderDefault,
+		"empty":      api.LoaderEmpty,
+		"file":       api.LoaderFile,
+		"global-css": api.LoaderGlobalCSS,
+		"js":         api.LoaderJS,
+		"json":       api.LoaderJSON,
+		"jsx":        api.LoaderJSX,
+		"local-css":  api.LoaderLocalCSS,
+		"text":       api.LoaderText,
+		"ts":         api.LoaderTS,
+		"tsx":        api.LoaderTSX,
+	}
+)
+
+// DecodeExternalOptions decodes the given map into ExternalOptions.
+func DecodeExternalOptions(m map[string]any) (ExternalOptions, error) {
+	opts := ExternalOptions{
+		SourcesContent: true,
+	}
+
+	if err := mapstructure.WeakDecode(m, &opts); err != nil {
+		return opts, err
+	}
+
+	if opts.TargetPath != "" {
+		opts.TargetPath = paths.ToSlashTrimLeading(opts.TargetPath)
+	}
+
+	opts.Target = strings.ToLower(opts.Target)
+	opts.Format = strings.ToLower(opts.Format)
+
+	return opts, nil
+}
+
+// ErrorMessageResolved holds a resolved error message.
+type ErrorMessageResolved struct {
+	Path    string
+	Message string
+	Content hugio.ReadSeekCloser
+}
+
+// ExternalOptions holds user facing options for the js.Build template function.
+type ExternalOptions struct {
+	// If not set, the source path will be used as the base target path.
+	// Note that the target path's extension may change if the target MIME type
+	// is different, e.g. when the source is TypeScript.
+	TargetPath string
+
+	// Whether to minify to output.
+	Minify bool
+
+	// One of "inline", "external", "linked" or "none".
+	SourceMap string
+
+	SourcesContent bool
+
+	// The language target.
+	// One of: es2015, es2016, es2017, es2018, es2019, es2020 or esnext.
+	// Default is esnext.
+	Target string
+
+	// The output format.
+	// One of: iife, cjs, esm
+	// Default is to esm.
+	Format string
+
+	// External dependencies, e.g. "react".
+	Externals []string
+
+	// This option allows you to automatically replace a global variable with an import from another file.
+	// The filenames must be relative to /assets.
+	// See https://esbuild.github.io/api/#inject
+	Inject []string
+
+	// User defined symbols.
+	Defines map[string]any
+
+	// Maps a component import to another.
+	Shims map[string]string
+
+	// Configuring a loader for a given file type lets you load that file type with an
+	// import statement or a require call. For example, configuring the .png file extension
+	// to use the data URL loader means importing a .png file gives you a data URL
+	// containing the contents of that image
+	//
+	// See https://esbuild.github.io/api/#loader
+	Loaders map[string]string
+
+	// User defined params. Will be marshaled to JSON and available as "@params", e.g.
+	//     import * as params from '@params';
+	Params any
+
+	// What to use instead of React.createElement.
+	JSXFactory string
+
+	// What to use instead of React.Fragment.
+	JSXFragment string
+
+	// What to do about JSX syntax.
+	// See https://esbuild.github.io/api/#jsx
+	JSX string
+
+	// Which library to use to automatically import JSX helper functions from. Only works if JSX is set to automatic.
+	// See https://esbuild.github.io/api/#jsx-import-source
+	JSXImportSource string
+
+	// There is/was a bug in WebKit with severe performance issue with the tracking
+	// of TDZ checks in JavaScriptCore.
+	//
+	// Enabling this flag removes the TDZ and `const` assignment checks and
+	// may improve performance of larger JS codebases until the WebKit fix
+	// is in widespread use.
+	//
+	// See https://bugs.webkit.org/show_bug.cgi?id=199866
+	// Deprecated: This no longer have any effect and will be removed.
+	// TODO(bep) remove. See https://github.com/evanw/esbuild/commit/869e8117b499ca1dbfc5b3021938a53ffe934dba
+	AvoidTDZ bool
+}
+
+// InternalOptions holds internal options for the js.Build template function.
+type InternalOptions struct {
+	MediaType     media.Type
+	OutDir        string
+	Contents      string
+	SourceDir     string
+	ResolveDir    string
+	AbsWorkingDir string
+	Metafile      bool
+
+	StdinSourcePath string
+
+	DependencyManager identity.Manager
+
+	Stdin                   bool // Set to true to pass in the entry point as a byte slice.
+	Splitting               bool
+	TsConfig                string
+	EntryPoints             []string
+	ImportOnResolveFunc     func(string, api.OnResolveArgs) string
+	ImportOnLoadFunc        func(api.OnLoadArgs) string
+	ImportParamsOnLoadFunc  func(args api.OnLoadArgs) json.RawMessage
+	ErrorMessageResolveFunc func(api.Message) *ErrorMessageResolved
+	ResolveSourceMapSource  func(string) string // Used to resolve paths in error source maps.
+}
+
+// Options holds the options passed to Build.
+type Options struct {
+	ExternalOptions
+	InternalOptions
+
+	compiled api.BuildOptions
+}
+
+func (opts *Options) compile() (err error) {
+	target, found := nameTarget[opts.Target]
+	if !found {
+		err = fmt.Errorf("invalid target: %q", opts.Target)
+		return
+	}
+
+	var loaders map[string]api.Loader
+	if opts.Loaders != nil {
+		loaders = make(map[string]api.Loader)
+		for k, v := range opts.Loaders {
+			loader, found := nameLoader[v]
+			if !found {
+				err = fmt.Errorf("invalid loader: %q", v)
+				return
+			}
+			loaders[k] = loader
+		}
+	}
+
+	mediaType := opts.MediaType
+	if mediaType.IsZero() {
+		mediaType = media.Builtin.JavascriptType
+	}
+
+	var loader api.Loader
+	switch mediaType.SubType {
+	case media.Builtin.JavascriptType.SubType:
+		loader = api.LoaderJS
+	case media.Builtin.TypeScriptType.SubType:
+		loader = api.LoaderTS
+	case media.Builtin.TSXType.SubType:
+		loader = api.LoaderTSX
+	case media.Builtin.JSXType.SubType:
+		loader = api.LoaderJSX
+	default:
+		err = fmt.Errorf("unsupported Media Type: %q", opts.MediaType)
+		return
+	}
+
+	var format api.Format
+	// One of: iife, cjs, esm
+	switch opts.Format {
+	case "", "iife":
+		format = api.FormatIIFE
+	case "esm":
+		format = api.FormatESModule
+	case "cjs":
+		format = api.FormatCommonJS
+	default:
+		err = fmt.Errorf("unsupported script output format: %q", opts.Format)
+		return
+	}
+
+	var jsx api.JSX
+	switch opts.JSX {
+	case "", "transform":
+		jsx = api.JSXTransform
+	case "preserve":
+		jsx = api.JSXPreserve
+	case "automatic":
+		jsx = api.JSXAutomatic
+	default:
+		err = fmt.Errorf("unsupported jsx type: %q", opts.JSX)
+		return
+	}
+
+	var defines map[string]string
+	if opts.Defines != nil {
+		defines = maps.ToStringMapString(opts.Defines)
+	}
+
+	// By default we only need to specify outDir and no outFile
+	outDir := opts.OutDir
+	outFile := ""
+	var sourceMap api.SourceMap
+	switch opts.SourceMap {
+	case "inline":
+		sourceMap = api.SourceMapInline
+	case "external":
+		sourceMap = api.SourceMapExternal
+	case "linked":
+		sourceMap = api.SourceMapLinked
+	case "", "none":
+		sourceMap = api.SourceMapNone
+	default:
+		err = fmt.Errorf("unsupported sourcemap type: %q", opts.SourceMap)
+		return
+	}
+
+	sourcesContent := api.SourcesContentInclude
+	if !opts.SourcesContent {
+		sourcesContent = api.SourcesContentExclude
+	}
+
+	opts.compiled = api.BuildOptions{
+		Outfile:       outFile,
+		Bundle:        true,
+		Metafile:      opts.Metafile,
+		AbsWorkingDir: opts.AbsWorkingDir,
+
+		Target:         target,
+		Format:         format,
+		Sourcemap:      sourceMap,
+		SourcesContent: sourcesContent,
+
+		Loader: loaders,
+
+		MinifyWhitespace:  opts.Minify,
+		MinifyIdentifiers: opts.Minify,
+		MinifySyntax:      opts.Minify,
+
+		Outdir:    outDir,
+		Splitting: opts.Splitting,
+
+		Define:   defines,
+		External: opts.Externals,
+
+		JSXFactory:  opts.JSXFactory,
+		JSXFragment: opts.JSXFragment,
+
+		JSX:             jsx,
+		JSXImportSource: opts.JSXImportSource,
+
+		Tsconfig: opts.TsConfig,
+
+		EntryPoints: opts.EntryPoints,
+	}
+
+	if opts.Stdin {
+		// This makes ESBuild pass `stdin` as the Importer to the import.
+		opts.compiled.Stdin = &api.StdinOptions{
+			Contents:   opts.Contents,
+			ResolveDir: opts.ResolveDir,
+			Loader:     loader,
+		}
+	}
+	return
+}
+
+func (o Options) loaderFromFilename(filename string) api.Loader {
+	ext := filepath.Ext(filename)
+	if optsLoaders := o.compiled.Loader; optsLoaders != nil {
+		if l, found := optsLoaders[ext]; found {
+			return l
+		}
+	}
+	l, found := extensionToLoaderMap[ext]
+	if found {
+		return l
+	}
+	return api.LoaderJS
+}
+
+func (opts *Options) validate() error {
+	if opts.ImportOnResolveFunc != nil && opts.ImportOnLoadFunc == nil {
+		return fmt.Errorf("ImportOnLoadFunc must be set if ImportOnResolveFunc is set")
+	}
+	if opts.ImportOnResolveFunc == nil && opts.ImportOnLoadFunc != nil {
+		return fmt.Errorf("ImportOnResolveFunc must be set if ImportOnLoadFunc is set")
+	}
+	if opts.AbsWorkingDir == "" {
+		return fmt.Errorf("AbsWorkingDir must be set")
+	}
+	return nil
+}
diff --git a/internal/js/esbuild/options_test.go b/internal/js/esbuild/options_test.go
new file mode 100644
index 000000000..ca19717f7
--- /dev/null
+++ b/internal/js/esbuild/options_test.go
@@ -0,0 +1,219 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package esbuild
+
+import (
+	"testing"
+
+	"github.com/gohugoio/hugo/media"
+
+	"github.com/evanw/esbuild/pkg/api"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestToBuildOptions(t *testing.T) {
+	c := qt.New(t)
+
+	opts := Options{
+		InternalOptions: InternalOptions{
+			MediaType: media.Builtin.JavascriptType,
+			Stdin:     true,
+		},
+	}
+
+	c.Assert(opts.compile(), qt.IsNil)
+	c.Assert(opts.compiled, qt.DeepEquals, api.BuildOptions{
+		Bundle:         true,
+		Target:         api.ESNext,
+		Format:         api.FormatIIFE,
+		SourcesContent: 1,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+	})
+
+	opts = Options{
+		ExternalOptions: ExternalOptions{
+			Target:   "es2018",
+			Format:   "cjs",
+			Minify:   true,
+			AvoidTDZ: true,
+		},
+		InternalOptions: InternalOptions{
+			MediaType: media.Builtin.JavascriptType,
+			Stdin:     true,
+		},
+	}
+
+	c.Assert(opts.compile(), qt.IsNil)
+	c.Assert(opts.compiled, qt.DeepEquals, api.BuildOptions{
+		Bundle:            true,
+		Target:            api.ES2018,
+		Format:            api.FormatCommonJS,
+		SourcesContent:    1,
+		MinifyIdentifiers: true,
+		MinifySyntax:      true,
+		MinifyWhitespace:  true,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+	})
+
+	opts = Options{
+		ExternalOptions: ExternalOptions{
+			Target: "es2018", Format: "cjs", Minify: true,
+			SourceMap: "inline",
+		},
+		InternalOptions: InternalOptions{
+			MediaType: media.Builtin.JavascriptType,
+			Stdin:     true,
+		},
+	}
+
+	c.Assert(opts.compile(), qt.IsNil)
+	c.Assert(opts.compiled, qt.DeepEquals, api.BuildOptions{
+		Bundle:            true,
+		Target:            api.ES2018,
+		Format:            api.FormatCommonJS,
+		MinifyIdentifiers: true,
+		MinifySyntax:      true,
+		MinifyWhitespace:  true,
+		SourcesContent:    1,
+		Sourcemap:         api.SourceMapInline,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+	})
+
+	opts = Options{
+		ExternalOptions: ExternalOptions{
+			Target: "es2018", Format: "cjs", Minify: true,
+			SourceMap: "inline",
+		},
+		InternalOptions: InternalOptions{
+			MediaType: media.Builtin.JavascriptType,
+			Stdin:     true,
+		},
+	}
+
+	c.Assert(opts.compile(), qt.IsNil)
+	c.Assert(opts.compiled, qt.DeepEquals, api.BuildOptions{
+		Bundle:            true,
+		Target:            api.ES2018,
+		Format:            api.FormatCommonJS,
+		MinifyIdentifiers: true,
+		MinifySyntax:      true,
+		MinifyWhitespace:  true,
+		Sourcemap:         api.SourceMapInline,
+		SourcesContent:    1,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+	})
+
+	opts = Options{
+		ExternalOptions: ExternalOptions{
+			Target: "es2018", Format: "cjs", Minify: true,
+			SourceMap: "external",
+		},
+		InternalOptions: InternalOptions{
+			MediaType: media.Builtin.JavascriptType,
+			Stdin:     true,
+		},
+	}
+
+	c.Assert(opts.compile(), qt.IsNil)
+	c.Assert(opts.compiled, qt.DeepEquals, api.BuildOptions{
+		Bundle:            true,
+		Target:            api.ES2018,
+		Format:            api.FormatCommonJS,
+		MinifyIdentifiers: true,
+		MinifySyntax:      true,
+		MinifyWhitespace:  true,
+		Sourcemap:         api.SourceMapExternal,
+		SourcesContent:    1,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+	})
+
+	opts = Options{
+		ExternalOptions: ExternalOptions{
+			JSX: "automatic", JSXImportSource: "preact",
+		},
+		InternalOptions: InternalOptions{
+			MediaType: media.Builtin.JavascriptType,
+			Stdin:     true,
+		},
+	}
+
+	c.Assert(opts.compile(), qt.IsNil)
+	c.Assert(opts.compiled, qt.DeepEquals, api.BuildOptions{
+		Bundle:         true,
+		Target:         api.ESNext,
+		Format:         api.FormatIIFE,
+		SourcesContent: 1,
+		Stdin: &api.StdinOptions{
+			Loader: api.LoaderJS,
+		},
+		JSX:             api.JSXAutomatic,
+		JSXImportSource: "preact",
+	})
+}
+
+func TestToBuildOptionsTarget(t *testing.T) {
+	c := qt.New(t)
+
+	for _, test := range []struct {
+		target string
+		expect api.Target
+	}{
+		{"es2015", api.ES2015},
+		{"es2016", api.ES2016},
+		{"es2017", api.ES2017},
+		{"es2018", api.ES2018},
+		{"es2019", api.ES2019},
+		{"es2020", api.ES2020},
+		{"es2021", api.ES2021},
+		{"es2022", api.ES2022},
+		{"es2023", api.ES2023},
+		{"", api.ESNext},
+		{"esnext", api.ESNext},
+	} {
+		c.Run(test.target, func(c *qt.C) {
+			opts := Options{
+				ExternalOptions: ExternalOptions{
+					Target: test.target,
+				},
+				InternalOptions: InternalOptions{
+					MediaType: media.Builtin.JavascriptType,
+				},
+			}
+
+			c.Assert(opts.compile(), qt.IsNil)
+			c.Assert(opts.compiled.Target, qt.Equals, test.expect)
+		})
+	}
+}
+
+func TestDecodeExternalOptions(t *testing.T) {
+	c := qt.New(t)
+	m := map[string]any{}
+	opts, err := DecodeExternalOptions(m)
+	c.Assert(err, qt.IsNil)
+	c.Assert(opts, qt.DeepEquals, ExternalOptions{
+		SourcesContent: true,
+	})
+}
diff --git a/internal/js/esbuild/resolve.go b/internal/js/esbuild/resolve.go
new file mode 100644
index 000000000..ac0010da9
--- /dev/null
+++ b/internal/js/esbuild/resolve.go
@@ -0,0 +1,315 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package esbuild
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/evanw/esbuild/pkg/api"
+	"github.com/gohugoio/hugo/common/maps"
+	"github.com/gohugoio/hugo/hugofs"
+	"github.com/gohugoio/hugo/identity"
+	"github.com/gohugoio/hugo/resources"
+	"github.com/gohugoio/hugo/resources/resource"
+	"github.com/spf13/afero"
+)
+
+const (
+	NsHugoImport            = "ns-hugo-imp"
+	NsHugoImportResolveFunc = "ns-hugo-imp-func"
+	nsHugoParams            = "ns-hugo-params"
+	pathHugoConfigParams    = "@params/config"
+
+	stdinImporter = "<stdin>"
+)
+
+var hugoNamespaces = []string{NsHugoImport, NsHugoImportResolveFunc, nsHugoParams}
+
+const (
+	PrefixHugoVirtual = "__hu_v"
+	PrefixHugoMemory  = "__hu_m"
+)
+
+var extensionToLoaderMap = map[string]api.Loader{
+	".js":   api.LoaderJS,
+	".mjs":  api.LoaderJS,
+	".cjs":  api.LoaderJS,
+	".jsx":  api.LoaderJSX,
+	".ts":   api.LoaderTS,
+	".tsx":  api.LoaderTSX,
+	".css":  api.LoaderCSS,
+	".json": api.LoaderJSON,
+	".txt":  api.LoaderText,
+}
+
+// This is a common sub-set of ESBuild's default extensions.
+// We assume that imports of JSON, CSS etc. will be using their full
+// name with extension.
+var commonExtensions = []string{".js", ".ts", ".tsx", ".jsx"}
+
+// ResolveComponent resolves a component using the given resolver.
+func ResolveComponent[T any](impPath string, resolve func(string) (v T, found, isDir bool)) (v T, found bool) {
+	findFirst := func(base string) (v T, found, isDir bool) {
+		for _, ext := range commonExtensions {
+			if strings.HasSuffix(impPath, ext) {
+				// Import of foo.js.js need the full name.
+				continue
+			}
+			if v, found, isDir = resolve(base + ext); found {
+				return
+			}
+		}
+
+		// Not found.
+		return
+	}
+
+	// We need to check if this is a regular file imported without an extension.
+	// There may be ambiguous situations where both foo.js and foo/index.js exists.
+	// This import order is in line with both how Node and ESBuild's native
+	// import resolver works.
+
+	// It may be a regular file imported without an extension, e.g.
+	// foo or foo/index.
+	v, found, _ = findFirst(impPath)
+	if found {
+		return v, found
+	}
+
+	base := filepath.Base(impPath)
+	if base == "index" {
+		// try index.esm.js etc.
+		v, found, _ = findFirst(impPath + ".esm")
+		if found {
+			return v, found
+		}
+	}
+
+	// Check the path as is.
+	var isDir bool
+	v, found, isDir = resolve(impPath)
+	if found && isDir {
+		v, found, _ = findFirst(filepath.Join(impPath, "index"))
+		if !found {
+			v, found, _ = findFirst(filepath.Join(impPath, "index.esm"))
+		}
+	}
+
+	if !found && strings.HasSuffix(base, ".js") {
+		v, found, _ = findFirst(strings.TrimSuffix(impPath, ".js"))
+	}
+
+	return
+}
+
+// ResolveResource resolves a resource using the given resourceGetter.
+func ResolveResource(impPath string, resourceGetter resource.ResourceGetter) (r resource.Resource) {
+	resolve := func(name string) (v resource.Resource, found, isDir bool) {
+		r := resourceGetter.Get(name)
+		return r, r != nil, false
+	}
+	r, found := ResolveComponent(impPath, resolve)
+	if !found {
+		return nil
+	}
+	return r
+}
+
+func newFSResolver(fs afero.Fs) *fsResolver {
+	return &fsResolver{fs: fs, resolved: maps.NewCache[string, *hugofs.FileMeta]()}
+}
+
+type fsResolver struct {
+	fs       afero.Fs
+	resolved *maps.Cache[string, *hugofs.FileMeta]
+}
+
+func (r *fsResolver) resolveComponent(impPath string) *hugofs.FileMeta {
+	v, _ := r.resolved.GetOrCreate(impPath, func() (*hugofs.FileMeta, error) {
+		resolve := func(name string) (*hugofs.FileMeta, bool, bool) {
+			if fi, err := r.fs.Stat(name); err == nil {
+				return fi.(hugofs.FileMetaInfo).Meta(), true, fi.IsDir()
+			}
+			return nil, false, false
+		}
+		v, _ := ResolveComponent(impPath, resolve)
+		return v, nil
+	})
+	return v
+}
+
+func createBuildPlugins(rs *resources.Spec, assetsResolver *fsResolver, depsManager identity.Manager, opts Options) ([]api.Plugin, error) {
+	fs := rs.Assets
+
+	resolveImport := func(args api.OnResolveArgs) (api.OnResolveResult, error) {
+		impPath := args.Path
+		shimmed := false
+		if opts.Shims != nil {
+			override, found := opts.Shims[impPath]
+			if found {
+				impPath = override
+				shimmed = true
+			}
+		}
+
+		if opts.ImportOnResolveFunc != nil {
+			if s := opts.ImportOnResolveFunc(impPath, args); s != "" {
+				return api.OnResolveResult{Path: s, Namespace: NsHugoImportResolveFunc}, nil
+			}
+		}
+
+		importer := args.Importer
+
+		isStdin := importer == stdinImporter
+		var relDir string
+		if !isStdin {
+			if strings.HasPrefix(importer, PrefixHugoVirtual) {
+				relDir = filepath.Dir(strings.TrimPrefix(importer, PrefixHugoVirtual))
+			} else {
+				rel, found := fs.MakePathRelative(importer, true)
+
+				if !found {
+					if shimmed {
+						relDir = opts.SourceDir
+					} else {
+						// Not in any of the /assets folders.
+						// This is an import from a node_modules, let
+						// ESBuild resolve this.
+						return api.OnResolveResult{}, nil
+					}
+				} else {
+					relDir = filepath.Dir(rel)
+				}
+			}
+		} else {
+			relDir = opts.SourceDir
+		}
+
+		// Imports not starting with a "." is assumed to live relative to /assets.
+		// Hugo makes no assumptions about the directory structure below /assets.
+		if relDir != "" && strings.HasPrefix(impPath, ".") {
+			impPath = filepath.Join(relDir, impPath)
+		}
+
+		m := assetsResolver.resolveComponent(impPath)
+
+		if m != nil {
+			depsManager.AddIdentity(m.PathInfo)
+
+			// Store the source root so we can create a jsconfig.json
+			// to help IntelliSense when the build is done.
+			// This should be a small number of elements, and when
+			// in server mode, we may get stale entries on renames etc.,
+			// but that shouldn't matter too much.
+			rs.JSConfigBuilder.AddSourceRoot(m.SourceRoot)
+			return api.OnResolveResult{Path: m.Filename, Namespace: NsHugoImport}, nil
+		}
+
+		// Fall back to ESBuild's resolve.
+		return api.OnResolveResult{}, nil
+	}
+
+	importResolver := api.Plugin{
+		Name: "hugo-import-resolver",
+		Setup: func(build api.PluginBuild) {
+			build.OnResolve(api.OnResolveOptions{Filter: `.*`},
+				func(args api.OnResolveArgs) (api.OnResolveResult, error) {
+					return resolveImport(args)
+				})
+			build.OnLoad(api.OnLoadOptions{Filter: `.*`, Namespace: NsHugoImport},
+				func(args api.OnLoadArgs) (api.OnLoadResult, error) {
+					b, err := os.ReadFile(args.Path)
+					if err != nil {
+						return api.OnLoadResult{}, fmt.Errorf("failed to read %q: %w", args.Path, err)
+					}
+					c := string(b)
+
+					return api.OnLoadResult{
+						// See https://github.com/evanw/esbuild/issues/502
+						// This allows all modules to resolve dependencies
+						// in the main project's node_modules.
+						ResolveDir: opts.ResolveDir,
+						Contents:   &c,
+						Loader:     opts.loaderFromFilename(args.Path),
+					}, nil
+				})
+			build.OnLoad(api.OnLoadOptions{Filter: `.*`, Namespace: NsHugoImportResolveFunc},
+				func(args api.OnLoadArgs) (api.OnLoadResult, error) {
+					c := opts.ImportOnLoadFunc(args)
+					if c == "" {
+						return api.OnLoadResult{}, fmt.Errorf("ImportOnLoadFunc failed to resolve %q", args.Path)
+					}
+
+					return api.OnLoadResult{
+						ResolveDir: opts.ResolveDir,
+						Contents:   &c,
+						Loader:     opts.loaderFromFilename(args.Path),
+					}, nil
+				})
+		},
+	}
+
+	params := opts.Params
+	if params == nil {
+		// This way @params will always resolve to something.
+		params = make(map[string]any)
+	}
+
+	b, err := json.Marshal(params)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal params: %w", err)
+	}
+
+	paramsPlugin := api.Plugin{
+		Name: "hugo-params-plugin",
+		Setup: func(build api.PluginBuild) {
+			build.OnResolve(api.OnResolveOptions{Filter: `^@params(/config)?$`},
+				func(args api.OnResolveArgs) (api.OnResolveResult, error) {
+					resolvedPath := args.Importer
+
+					if args.Path == pathHugoConfigParams {
+						resolvedPath = pathHugoConfigParams
+					}
+
+					return api.OnResolveResult{
+						Path:      resolvedPath,
+						Namespace: nsHugoParams,
+					}, nil
+				})
+			build.OnLoad(api.OnLoadOptions{Filter: `.*`, Namespace: nsHugoParams},
+				func(args api.OnLoadArgs) (api.OnLoadResult, error) {
+					bb := b
+					if args.Path != pathHugoConfigParams && opts.ImportParamsOnLoadFunc != nil {
+						bb = opts.ImportParamsOnLoadFunc(args)
+					}
+					s := string(bb)
+
+					if s == "" {
+						s = "{}"
+					}
+
+					return api.OnLoadResult{
+						Contents: &s,
+						Loader:   api.LoaderJSON,
+					}, nil
+				})
+		},
+	}
+
+	return []api.Plugin{importResolver, paramsPlugin}, nil
+}
diff --git a/internal/js/esbuild/resolve_test.go b/internal/js/esbuild/resolve_test.go
new file mode 100644
index 000000000..86e3138f2
--- /dev/null
+++ b/internal/js/esbuild/resolve_test.go
@@ -0,0 +1,86 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package esbuild
+
+import (
+	"path"
+	"path/filepath"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+	"github.com/gohugoio/hugo/config"
+	"github.com/gohugoio/hugo/config/testconfig"
+	"github.com/gohugoio/hugo/hugofs"
+	"github.com/gohugoio/hugo/hugolib/filesystems"
+	"github.com/gohugoio/hugo/hugolib/paths"
+	"github.com/spf13/afero"
+)
+
+func TestResolveComponentInAssets(t *testing.T) {
+	c := qt.New(t)
+
+	for _, test := range []struct {
+		name    string
+		files   []string
+		impPath string
+		expect  string
+	}{
+		{"Basic, extension", []string{"foo.js", "bar.js"}, "foo.js", "foo.js"},
+		{"Basic, no extension", []string{"foo.js", "bar.js"}, "foo", "foo.js"},
+		{"Basic, no extension, typescript", []string{"foo.ts", "bar.js"}, "foo", "foo.ts"},
+		{"Not found", []string{"foo.js", "bar.js"}, "moo.js", ""},
+		{"Not found, double js extension", []string{"foo.js.js", "bar.js"}, "foo.js", ""},
+		{"Index file, folder only", []string{"foo/index.js", "bar.js"}, "foo", "foo/index.js"},
+		{"Index file, folder and index", []string{"foo/index.js", "bar.js"}, "foo/index", "foo/index.js"},
+		{"Index file, folder and index and suffix", []string{"foo/index.js", "bar.js"}, "foo/index.js", "foo/index.js"},
+		{"Index ESM file, folder only", []string{"foo/index.esm.js", "bar.js"}, "foo", "foo/index.esm.js"},
+		{"Index ESM file, folder and index", []string{"foo/index.esm.js", "bar.js"}, "foo/index", "foo/index.esm.js"},
+		{"Index ESM file, folder and index and suffix", []string{"foo/index.esm.js", "bar.js"}, "foo/index.esm.js", "foo/index.esm.js"},
+		// We added these index.esm.js cases in v0.101.0. The case below is unlikely to happen in the wild, but add a test
+		// to document Hugo's behavior. We pick the file with the name index.js; anything else would be breaking.
+		{"Index and Index ESM file, folder only", []string{"foo/index.esm.js", "foo/index.js", "bar.js"}, "foo", "foo/index.js"},
+
+		// Issue #8949
+		{"Check file before directory", []string{"foo.js", "foo/index.js"}, "foo", "foo.js"},
+	} {
+		c.Run(test.name, func(c *qt.C) {
+			baseDir := "assets"
+			mfs := afero.NewMemMapFs()
+
+			for _, filename := range test.files {
+				c.Assert(afero.WriteFile(mfs, filepath.Join(baseDir, filename), []byte("let foo='bar';"), 0o777), qt.IsNil)
+			}
+
+			conf := testconfig.GetTestConfig(mfs, config.New())
+			fs := hugofs.NewFrom(mfs, conf.BaseConfig())
+
+			p, err := paths.New(fs, conf)
+			c.Assert(err, qt.IsNil)
+			bfs, err := filesystems.NewBase(p, nil)
+			c.Assert(err, qt.IsNil)
+			resolver := newFSResolver(bfs.Assets.Fs)
+
+			got := resolver.resolveComponent(test.impPath)
+
+			gotPath := ""
+			expect := test.expect
+			if got != nil {
+				gotPath = filepath.ToSlash(got.Filename)
+				expect = path.Join(baseDir, test.expect)
+			}
+
+			c.Assert(gotPath, qt.Equals, expect)
+		})
+	}
+}
diff --git a/internal/js/esbuild/sourcemap.go b/internal/js/esbuild/sourcemap.go
new file mode 100644
index 000000000..647f0c081
--- /dev/null
+++ b/internal/js/esbuild/sourcemap.go
@@ -0,0 +1,80 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package esbuild
+
+import (
+	"encoding/json"
+	"strings"
+
+	"github.com/evanw/esbuild/pkg/api"
+	"github.com/gohugoio/hugo/common/paths"
+)
+
+type sourceMap struct {
+	Version        int      `json:"version"`
+	Sources        []string `json:"sources"`
+	SourcesContent []string `json:"sourcesContent"`
+	Mappings       string   `json:"mappings"`
+	Names          []string `json:"names"`
+}
+
+func fixOutputFile(o *api.OutputFile, resolve func(string) string) error {
+	if strings.HasSuffix(o.Path, ".map") {
+		b, err := fixSourceMap(o.Contents, resolve)
+		if err != nil {
+			return err
+		}
+		o.Contents = b
+	}
+	return nil
+}
+
+func fixSourceMap(s []byte, resolve func(string) string) ([]byte, error) {
+	var sm sourceMap
+	if err := json.Unmarshal([]byte(s), &sm); err != nil {
+		return nil, err
+	}
+
+	sm.Sources = fixSourceMapSources(sm.Sources, resolve)
+
+	b, err := json.Marshal(sm)
+	if err != nil {
+		return nil, err
+	}
+
+	return b, nil
+}
+
+func fixSourceMapSources(s []string, resolve func(string) string) []string {
+	var result []string
+	for _, src := range s {
+		if s := resolve(src); s != "" {
+			// Absolute filenames works fine on U*ix (tested in Chrome on MacOs), but works very poorly on Windows (again Chrome).
+			// So, convert it to a URL.
+			if u, err := paths.UrlFromFilename(s); err == nil {
+				result = append(result, u.String())
+			}
+		}
+	}
+	return result
+}
+
+// Used in tests.
+func SourcesFromSourceMap(s string) []string {
+	var sm sourceMap
+	if err := json.Unmarshal([]byte(s), &sm); err != nil {
+		return nil
+	}
+	return sm.Sources
+}
diff --git a/lazy/init.go b/lazy/init.go
index 7b88a5351..bef3867a9 100644
--- a/lazy/init.go
+++ b/lazy/init.go
@@ -36,7 +36,7 @@ type Init struct {
 	prev     *Init
 	children []*Init
 
-	init onceMore
+	init OnceMore
 	out  any
 	err  error
 	f    func(context.Context) (any, error)
diff --git a/lazy/once.go b/lazy/once.go
index cea096652..dac689df3 100644
--- a/lazy/once.go
+++ b/lazy/once.go
@@ -24,13 +24,13 @@ import (
 // * it can be reset, so the action can be repeated if needed
 // * it has methods to check if it's done or in progress
 
-type onceMore struct {
+type OnceMore struct {
 	mu   sync.Mutex
 	lock uint32
 	done uint32
 }
 
-func (t *onceMore) Do(f func()) {
+func (t *OnceMore) Do(f func()) {
 	if atomic.LoadUint32(&t.done) == 1 {
 		return
 	}
@@ -53,15 +53,15 @@ func (t *onceMore) Do(f func()) {
 	f()
 }
 
-func (t *onceMore) InProgress() bool {
+func (t *OnceMore) InProgress() bool {
 	return atomic.LoadUint32(&t.lock) == 1
 }
 
-func (t *onceMore) Done() bool {
+func (t *OnceMore) Done() bool {
 	return atomic.LoadUint32(&t.done) == 1
 }
 
-func (t *onceMore) ResetWithLock() *sync.Mutex {
+func (t *OnceMore) ResetWithLock() *sync.Mutex {
 	t.mu.Lock()
 	defer atomic.StoreUint32(&t.done, 0)
 	return &t.mu
diff --git a/media/mediaType.go b/media/mediaType.go
index a7ba1309a..97b10879c 100644
--- a/media/mediaType.go
+++ b/media/mediaType.go
@@ -273,9 +273,13 @@ func (t Types) GetByType(tp string) (Type, bool) {
 	return Type{}, false
 }
 
+func (t Types) normalizeSuffix(s string) string {
+	return strings.ToLower(strings.TrimPrefix(s, "."))
+}
+
 // BySuffix will return all media types matching a suffix.
 func (t Types) BySuffix(suffix string) []Type {
-	suffix = strings.ToLower(suffix)
+	suffix = t.normalizeSuffix(suffix)
 	var types []Type
 	for _, tt := range t {
 		if tt.hasSuffix(suffix) {
@@ -287,7 +291,7 @@ func (t Types) BySuffix(suffix string) []Type {
 
 // GetFirstBySuffix will return the first type matching the given suffix.
 func (t Types) GetFirstBySuffix(suffix string) (Type, SuffixInfo, bool) {
-	suffix = strings.ToLower(suffix)
+	suffix = t.normalizeSuffix(suffix)
 	for _, tt := range t {
 		if tt.hasSuffix(suffix) {
 			return tt, SuffixInfo{
@@ -304,7 +308,7 @@ func (t Types) GetFirstBySuffix(suffix string) (Type, SuffixInfo, bool) {
 // is ambiguous.
 // The lookup is case insensitive.
 func (t Types) GetBySuffix(suffix string) (tp Type, si SuffixInfo, found bool) {
-	suffix = strings.ToLower(suffix)
+	suffix = t.normalizeSuffix(suffix)
 	for _, tt := range t {
 		if tt.hasSuffix(suffix) {
 			if found {
@@ -324,7 +328,7 @@ func (t Types) GetBySuffix(suffix string) (tp Type, si SuffixInfo, found bool) {
 }
 
 func (t Types) IsTextSuffix(suffix string) bool {
-	suffix = strings.ToLower(suffix)
+	suffix = t.normalizeSuffix(suffix)
 	for _, tt := range t {
 		if tt.hasSuffix(suffix) {
 			return tt.IsText()
diff --git a/resources/image.go b/resources/image.go
index 4595866d4..686f70e27 100644
--- a/resources/image.go
+++ b/resources/image.go
@@ -51,6 +51,7 @@ var (
 	_ resource.Source                 = (*imageResource)(nil)
 	_ resource.Cloner                 = (*imageResource)(nil)
 	_ resource.NameNormalizedProvider = (*imageResource)(nil)
+	_ targetPathProvider              = (*imageResource)(nil)
 )
 
 // imageResource represents an image resource.
@@ -160,6 +161,10 @@ func (i *imageResource) Colors() ([]images.Color, error) {
 	return i.dominantColors, nil
 }
 
+func (i *imageResource) targetPath() string {
+	return i.TargetPath()
+}
+
 // Clone is for internal use.
 func (i *imageResource) Clone() resource.Resource {
 	gr := i.baseResource.Clone().(baseResource)
diff --git a/resources/page/page.go b/resources/page/page.go
index 032ee320d..40e15dc6f 100644
--- a/resources/page/page.go
+++ b/resources/page/page.go
@@ -63,8 +63,7 @@ type ChildCareProvider interface {
 	// section.
 	RegularPagesRecursive() Pages
 
-	// Resources returns a list of all resources.
-	Resources() resource.Resources
+	resource.ResourcesProvider
 }
 
 type MarkupProvider interface {
diff --git a/resources/resource.go b/resources/resource.go
index cc7008e5a..6025cbf4c 100644
--- a/resources/resource.go
+++ b/resources/resource.go
@@ -47,6 +47,8 @@ var (
 	_ resource.Cloner                    = (*genericResource)(nil)
 	_ resource.ResourcesLanguageMerger   = (*resource.Resources)(nil)
 	_ resource.Identifier                = (*genericResource)(nil)
+	_ targetPathProvider                 = (*genericResource)(nil)
+	_ sourcePathProvider                 = (*genericResource)(nil)
 	_ identity.IdentityGroupProvider     = (*genericResource)(nil)
 	_ identity.DependencyManagerProvider = (*genericResource)(nil)
 	_ identity.Identity                  = (*genericResource)(nil)
@@ -79,6 +81,7 @@ type ResourceSourceDescriptor struct {
 	TargetPath           string
 	BasePathRelPermalink string
 	BasePathTargetPath   string
+	SourceFilenameOrPath string // Used for error logging.
 
 	// The Data to associate with this resource.
 	Data map[string]any
@@ -463,6 +466,17 @@ func (l *genericResource) Key() string {
 	return key
 }
 
+func (l *genericResource) targetPath() string {
+	return l.paths.TargetPath()
+}
+
+func (l *genericResource) sourcePath() string {
+	if p := l.sd.SourceFilenameOrPath; p != "" {
+		return p
+	}
+	return ""
+}
+
 func (l *genericResource) MediaType() media.Type {
 	return l.sd.MediaType
 }
@@ -660,3 +674,43 @@ func (r *resourceHash) init(l hugio.ReadSeekCloserProvider) error {
 func hashImage(r io.ReadSeeker) (uint64, int64, error) {
 	return hashing.XXHashFromReader(r)
 }
+
+// InternalResourceTargetPath is used internally to get the target path for a Resource.
+func InternalResourceTargetPath(r resource.Resource) string {
+	return r.(targetPathProvider).targetPath()
+}
+
+// InternalResourceSourcePathBestEffort is used internally to get the source path for a Resource.
+// It returns an empty string if the source path is not available.
+func InternalResourceSourcePath(r resource.Resource) string {
+	if sp, ok := r.(sourcePathProvider); ok {
+		if p := sp.sourcePath(); p != "" {
+			return p
+		}
+	}
+	return ""
+}
+
+// InternalResourceSourcePathBestEffort is used internally to get the source path for a Resource.
+// Used for error messages etc.
+// It will fall back to the target path if the source path is not available.
+func InternalResourceSourcePathBestEffort(r resource.Resource) string {
+	if s := InternalResourceSourcePath(r); s != "" {
+		return s
+	}
+	return InternalResourceTargetPath(r)
+}
+
+type targetPathProvider interface {
+	// targetPath is the relative path to this resource.
+	// In most cases this will be the same as the RelPermalink(),
+	// but it will not trigger any lazy publishing.
+	targetPath() string
+}
+
+// Optional interface implemented by resources that can provide the source path.
+type sourcePathProvider interface {
+	// sourcePath is the source path to this resource's source.
+	// This is used in error messages etc.
+	sourcePath() string
+}
diff --git a/resources/resource/resource_helpers.go b/resources/resource/resource_helpers.go
index c2bb463c8..8575ae79e 100644
--- a/resources/resource/resource_helpers.go
+++ b/resources/resource/resource_helpers.go
@@ -14,10 +14,11 @@
 package resource
 
 import (
-	"github.com/gohugoio/hugo/common/maps"
 	"strings"
 	"time"
 
+	"github.com/gohugoio/hugo/common/maps"
+
 	"github.com/gohugoio/hugo/helpers"
 	"github.com/pelletier/go-toml/v2"
 
diff --git a/resources/resource/resources.go b/resources/resource/resources.go
index 32bcdbb08..480c703b5 100644
--- a/resources/resource/resources.go
+++ b/resources/resource/resources.go
@@ -16,8 +16,11 @@ package resource
 
 import (
 	"fmt"
+	"path"
 	"strings"
 
+	"github.com/gohugoio/hugo/common/hreflect"
+	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/common/paths"
 	"github.com/gohugoio/hugo/hugofs/glob"
 	"github.com/spf13/cast"
@@ -29,6 +32,51 @@ var _ ResourceFinder = (*Resources)(nil)
 // I.e. both pages and images etc.
 type Resources []Resource
 
+// Mount mounts the given resources from base to the given target path.
+// Note that leading slashes in target marks an absolute path.
+// This method is currently only useful in js.Batch.
+func (r Resources) Mount(base, target string) ResourceGetter {
+	return resourceGetterFunc(func(namev any) Resource {
+		name1, err := cast.ToStringE(namev)
+		if err != nil {
+			panic(err)
+		}
+
+		isTargetAbs := strings.HasPrefix(target, "/")
+
+		if target != "" {
+			name1 = strings.TrimPrefix(name1, target)
+			if !isTargetAbs {
+				name1 = paths.TrimLeading(name1)
+			}
+		}
+
+		if base != "" && isTargetAbs {
+			name1 = path.Join(base, name1)
+		}
+
+		for _, res := range r {
+			name2 := res.Name()
+
+			if base != "" && !isTargetAbs {
+				name2 = paths.TrimLeading(strings.TrimPrefix(name2, base))
+			}
+
+			if strings.EqualFold(name1, name2) {
+				return res
+			}
+
+		}
+
+		return nil
+	})
+}
+
+type ResourcesProvider interface {
+	// Resources returns a list of all resources.
+	Resources() Resources
+}
+
 // var _ resource.ResourceFinder = (*Namespace)(nil)
 // ResourcesConverter converts a given slice of Resource objects to Resources.
 type ResourcesConverter interface {
@@ -63,13 +111,25 @@ func (r Resources) Get(name any) Resource {
 		panic(err)
 	}
 
-	namestr = paths.AddLeadingSlash(namestr)
+	isDotCurrent := strings.HasPrefix(namestr, "./")
+	if isDotCurrent {
+		namestr = strings.TrimPrefix(namestr, "./")
+	} else {
+		namestr = paths.AddLeadingSlash(namestr)
+	}
+
+	check := func(name string) bool {
+		if !isDotCurrent {
+			name = paths.AddLeadingSlash(name)
+		}
+		return strings.EqualFold(namestr, name)
+	}
 
 	// First check the Name.
 	// Note that this can be modified by the user in the front matter,
 	// also, it does not contain any language code.
 	for _, resource := range r {
-		if strings.EqualFold(namestr, paths.AddLeadingSlash(resource.Name())) {
+		if check(resource.Name()) {
 			return resource
 		}
 	}
@@ -77,7 +137,7 @@ func (r Resources) Get(name any) Resource {
 	// Finally, check the normalized name.
 	for _, resource := range r {
 		if nop, ok := resource.(NameNormalizedProvider); ok {
-			if strings.EqualFold(namestr, paths.AddLeadingSlash(nop.NameNormalized())) {
+			if check(nop.NameNormalized()) {
 				return resource
 			}
 		}
@@ -197,14 +257,35 @@ type Source interface {
 	Publish() error
 }
 
-// ResourceFinder provides methods to find Resources.
-// Note that GetRemote (as found in resources.GetRemote) is
-// not covered by this interface, as this is only available as a global template function.
-type ResourceFinder interface {
+type ResourceGetter interface {
 	// Get locates the Resource with the given name in the current context (e.g. in .Page.Resources).
 	//
 	// It returns nil if no Resource could found, panics if name is invalid.
 	Get(name any) Resource
+}
+
+type IsProbablySameResourceGetter interface {
+	IsProbablySameResourceGetter(other ResourceGetter) bool
+}
+
+// StaleInfoResourceGetter is a ResourceGetter that also provides information about
+// whether the underlying resources are stale.
+type StaleInfoResourceGetter interface {
+	StaleInfo
+	ResourceGetter
+}
+
+type resourceGetterFunc func(name any) Resource
+
+func (f resourceGetterFunc) Get(name any) Resource {
+	return f(name)
+}
+
+// ResourceFinder provides methods to find Resources.
+// Note that GetRemote (as found in resources.GetRemote) is
+// not covered by this interface, as this is only available as a global template function.
+type ResourceFinder interface {
+	ResourceGetter
 
 	// GetMatch finds the first Resource matching the given pattern, or nil if none found.
 	//
@@ -235,3 +316,92 @@ type ResourceFinder interface {
 	// It returns nil if no Resources could found, panics if typ is invalid.
 	ByType(typ any) Resources
 }
+
+// NewCachedResourceGetter creates a new ResourceGetter from the given objects.
+// If multiple objects are provided, they are merged into one where
+// the first match wins.
+func NewCachedResourceGetter(os ...any) *cachedResourceGetter {
+	var getters multiResourceGetter
+	for _, o := range os {
+		if g, ok := unwrapResourceGetter(o); ok {
+			getters = append(getters, g)
+		}
+	}
+
+	return &cachedResourceGetter{
+		cache:    maps.NewCache[string, Resource](),
+		delegate: getters,
+	}
+}
+
+type multiResourceGetter []ResourceGetter
+
+func (m multiResourceGetter) Get(name any) Resource {
+	for _, g := range m {
+		if res := g.Get(name); res != nil {
+			return res
+		}
+	}
+	return nil
+}
+
+var (
+	_ ResourceGetter               = (*cachedResourceGetter)(nil)
+	_ IsProbablySameResourceGetter = (*cachedResourceGetter)(nil)
+)
+
+type cachedResourceGetter struct {
+	cache    *maps.Cache[string, Resource]
+	delegate ResourceGetter
+}
+
+func (c *cachedResourceGetter) Get(name any) Resource {
+	namestr, err := cast.ToStringE(name)
+	if err != nil {
+		panic(err)
+	}
+	v, _ := c.cache.GetOrCreate(namestr, func() (Resource, error) {
+		v := c.delegate.Get(name)
+		return v, nil
+	})
+	return v
+}
+
+func (c *cachedResourceGetter) IsProbablySameResourceGetter(other ResourceGetter) bool {
+	isProbablyEq := true
+	c.cache.ForEeach(func(k string, v Resource) bool {
+		if v != other.Get(k) {
+			isProbablyEq = false
+			return false
+		}
+		return true
+	})
+
+	return isProbablyEq
+}
+
+func unwrapResourceGetter(v any) (ResourceGetter, bool) {
+	if v == nil {
+		return nil, false
+	}
+	switch vv := v.(type) {
+	case ResourceGetter:
+		return vv, true
+	case ResourcesProvider:
+		return vv.Resources(), true
+	case func(name any) Resource:
+		return resourceGetterFunc(vv), true
+	default:
+		vvv, ok := hreflect.ToSliceAny(v)
+		if !ok {
+			return nil, false
+		}
+		var getters multiResourceGetter
+		for _, vv := range vvv {
+			if g, ok := unwrapResourceGetter(vv); ok {
+				getters = append(getters, g)
+			}
+		}
+		return getters, len(getters) > 0
+	}
+}
diff --git a/resources/resource/resources_integration_test.go b/resources/resource/resources_integration_test.go
new file mode 100644
index 000000000..920fc7397
--- /dev/null
+++ b/resources/resource/resources_integration_test.go
@@ -0,0 +1,105 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package resource_test
+
+import (
+	"testing"
+
+	"github.com/gohugoio/hugo/hugolib"
+)
+
+func TestResourcesMount(t *testing.T) {
+	files := `
+-- hugo.toml --
+-- assets/text/txt1.txt --
+Text 1.
+-- assets/text/txt2.txt --
+Text 2.
+-- assets/text/sub/txt3.txt --
+Text 3.
+-- assets/text/sub/txt4.txt --
+Text 4.
+-- content/mybundle/index.md --
+---
+title: "My Bundle"
+---
+-- content/mybundle/txt1.txt --
+Text 1.
+-- content/mybundle/sub/txt2.txt --
+Text 1.
+-- layouts/index.html --
+{{ $mybundle := site.GetPage "mybundle" }}
+{{ $subResources := resources.Match "/text/sub/*.*"  }}
+{{ $subResourcesMount :=  $subResources.Mount "/text/sub" "/newroot" }}
+resources:text/txt1.txt:{{ with resources.Get "text/txt1.txt" }}{{ .Name }}{{ end }}|
+resources:text/txt2.txt:{{ with resources.Get "text/txt2.txt" }}{{ .Name }}{{ end }}|
+resources:text/sub/txt3.txt:{{ with resources.Get "text/sub/txt3.txt" }}{{ .Name }}{{ end }}|
+subResources.range:{{ range $subResources }}{{ .Name }}|{{ end }}|
+subResources:"text/sub/txt3.txt:{{ with $subResources.Get "text/sub/txt3.txt" }}{{ .Name }}{{ end }}|
+subResourcesMount:/newroot/txt3.txt:{{ with $subResourcesMount.Get "/newroot/txt3.txt" }}{{ .Name }}{{ end }}|
+page:txt1.txt:{{ with $mybundle.Resources.Get "txt1.txt" }}{{ .Name }}{{ end }}|
+page:./txt1.txt:{{ with $mybundle.Resources.Get "./txt1.txt" }}{{ .Name }}{{ end }}|
+page:sub/txt2.txt:{{ with $mybundle.Resources.Get "sub/txt2.txt" }}{{ .Name }}{{ end }}|
+`
+	b := hugolib.Test(t, files)
+
+	b.AssertFileContent("public/index.html", `
+resources:text/txt1.txt:/text/txt1.txt|
+resources:text/txt2.txt:/text/txt2.txt|
+resources:text/sub/txt3.txt:/text/sub/txt3.txt|
+subResources:"text/sub/txt3.txt:/text/sub/txt3.txt|
+subResourcesMount:/newroot/txt3.txt:/text/sub/txt3.txt|
+page:txt1.txt:txt1.txt|
+page:./txt1.txt:txt1.txt|
+page:sub/txt2.txt:sub/txt2.txt|
+`)
+}
+
+func TestResourcesMountOnRename(t *testing.T) {
+	files := `
+-- hugo.toml --
+disableKinds = ["taxonomy", "term", "home", "sitemap"]
+-- content/mybundle/index.md --
+---
+title: "My Bundle"
+resources:
+- name: /foo/bars.txt
+  src: foo/txt1.txt
+- name: foo/bars2.txt
+  src: foo/txt2.txt
+---
+-- content/mybundle/foo/txt1.txt --
+Text 1.
+-- content/mybundle/foo/txt2.txt --
+Text 2.
+-- layouts/_default/single.html --
+Single.
+{{ $mybundle := site.GetPage "mybundle" }}
+Resources:{{ range $mybundle.Resources }}Name: {{ .Name }}|{{ end }}$
+{{ $subResourcesMount :=  $mybundle.Resources.Mount "/foo" "/newroot" }}
+ {{ $subResourcesMount2 :=  $mybundle.Resources.Mount "foo" "/newroot" }}
+{{ $subResourcesMount3 :=  $mybundle.Resources.Mount "foo" "." }}
+subResourcesMount:/newroot/bars.txt:{{ with $subResourcesMount.Get "/newroot/bars.txt" }}{{ .Name }}{{ end }}|
+subResourcesMount:/newroot/bars2.txt:{{ with $subResourcesMount.Get "/newroot/bars2.txt" }}{{ .Name }}{{ end }}|
+subResourcesMount2:/newroot/bars2.txt:{{ with $subResourcesMount2.Get "/newroot/bars2.txt" }}{{ .Name }}{{ end }}|
+subResourcesMount3:bars2.txt:{{ with $subResourcesMount3.Get "bars2.txt" }}{{ .Name }}{{ end }}|
+`
+	b := hugolib.Test(t, files)
+	b.AssertFileContent("public/mybundle/index.html",
+		"Resources:Name: foo/bars.txt|Name: foo/bars2.txt|$",
+		"subResourcesMount:/newroot/bars.txt:|\nsubResourcesMount:/newroot/bars2.txt:|",
+		"subResourcesMount2:/newroot/bars2.txt:foo/bars2.txt|",
+		"subResourcesMount3:bars2.txt:foo/bars2.txt|",
+	)
+}
diff --git a/resources/resource/resources_test.go b/resources/resource/resources_test.go
new file mode 100644
index 000000000..ebadbb312
--- /dev/null
+++ b/resources/resource/resources_test.go
@@ -0,0 +1,122 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package resource
+
+import (
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestResourcesMount(t *testing.T) {
+	c := qt.New(t)
+	c.Assert(true, qt.IsTrue)
+
+	var m ResourceGetter
+	var r Resources
+
+	check := func(in, expect string) {
+		c.Helper()
+		r := m.Get(in)
+		c.Assert(r, qt.Not(qt.IsNil))
+		c.Assert(r.Name(), qt.Equals, expect)
+	}
+
+	checkNil := func(in string) {
+		c.Helper()
+		r := m.Get(in)
+		c.Assert(r, qt.IsNil)
+	}
+
+	// Misc tests.
+	r = Resources{
+		testResource{name: "/foo/theme.css"},
+	}
+
+	m = r.Mount("/foo", ".")
+	check("./theme.css", "/foo/theme.css")
+
+	// Relative target.
+	r = Resources{
+		testResource{name: "/a/b/c/d.txt"},
+		testResource{name: "/a/b/c/e/f.txt"},
+		testResource{name: "/a/b/d.txt"},
+		testResource{name: "/a/b/e.txt"},
+	}
+
+	m = r.Mount("/a/b/c", "z")
+	check("z/d.txt", "/a/b/c/d.txt")
+	check("z/e/f.txt", "/a/b/c/e/f.txt")
+
+	m = r.Mount("/a/b", "")
+	check("d.txt", "/a/b/d.txt")
+	m = r.Mount("/a/b", ".")
+	check("d.txt", "/a/b/d.txt")
+	m = r.Mount("/a/b", "./")
+	check("d.txt", "/a/b/d.txt")
+	check("./d.txt", "/a/b/d.txt")
+
+	m = r.Mount("/a/b", ".")
+	check("./d.txt", "/a/b/d.txt")
+
+	// Absolute target.
+	m = r.Mount("/a/b/c", "/z")
+	check("/z/d.txt", "/a/b/c/d.txt")
+	check("/z/e/f.txt", "/a/b/c/e/f.txt")
+	checkNil("/z/f.txt")
+
+	m = r.Mount("/a/b", "/z")
+	check("/z/c/d.txt", "/a/b/c/d.txt")
+	check("/z/c/e/f.txt", "/a/b/c/e/f.txt")
+	check("/z/d.txt", "/a/b/d.txt")
+	checkNil("/z/f.txt")
+
+	m = r.Mount("", "")
+	check("/a/b/c/d.txt", "/a/b/c/d.txt")
+	check("/a/b/c/e/f.txt", "/a/b/c/e/f.txt")
+	check("/a/b/d.txt", "/a/b/d.txt")
+	checkNil("/a/b/f.txt")
+
+	m = r.Mount("/a/b", "/a/b")
+	check("/a/b/c/d.txt", "/a/b/c/d.txt")
+	check("/a/b/c/e/f.txt", "/a/b/c/e/f.txt")
+	check("/a/b/d.txt", "/a/b/d.txt")
+	checkNil("/a/b/f.txt")
+
+	// Resources with relative paths.
+	r = Resources{
+		testResource{name: "a/b/c/d.txt"},
+		testResource{name: "a/b/c/e/f.txt"},
+		testResource{name: "a/b/d.txt"},
+		testResource{name: "a/b/e.txt"},
+		testResource{name: "n.txt"},
+	}
+
+	m = r.Mount("a/b", "z")
+	check("z/d.txt", "a/b/d.txt")
+	checkNil("/z/d.txt")
+}
+
+type testResource struct {
+	Resource
+	name string
+}
+
+func (r testResource) Name() string {
+	return r.name
+}
+
+func (r testResource) NameNormalized() string {
+	return r.name
+}
diff --git a/resources/resource_factories/create/create.go b/resources/resource_factories/create/create.go
index 2d868bd15..7dd26f4c0 100644
--- a/resources/resource_factories/create/create.go
+++ b/resources/resource_factories/create/create.go
@@ -143,16 +143,18 @@ func (c *Client) Get(pathname string) (resource.Resource, error) {
 			return nil, err
 		}
 
-		pi := fi.(hugofs.FileMetaInfo).Meta().PathInfo
+		meta := fi.(hugofs.FileMetaInfo).Meta()
+		pi := meta.PathInfo
 
 		return c.rs.NewResource(resources.ResourceSourceDescriptor{
 			LazyPublish: true,
 			OpenReadSeekCloser: func() (hugio.ReadSeekCloser, error) {
 				return c.rs.BaseFs.Assets.Fs.Open(filename)
 			},
-			Path:          pi,
-			GroupIdentity: pi,
-			TargetPath:    pathname,
+			Path:                 pi,
+			GroupIdentity:        pi,
+			TargetPath:           pathname,
+			SourceFilenameOrPath: meta.Filename,
 		})
 	})
 }
@@ -196,10 +198,11 @@ func (c *Client) match(name, pattern string, matchFunc func(r resource.Resource)
 				OpenReadSeekCloser: func() (hugio.ReadSeekCloser, error) {
 					return meta.Open()
 				},
-				NameNormalized: meta.PathInfo.Path(),
-				NameOriginal:   meta.PathInfo.Unnormalized().Path(),
-				GroupIdentity:  meta.PathInfo,
-				TargetPath:     meta.PathInfo.Unnormalized().Path(),
+				NameNormalized:       meta.PathInfo.Path(),
+				NameOriginal:         meta.PathInfo.Unnormalized().Path(),
+				GroupIdentity:        meta.PathInfo,
+				TargetPath:           meta.PathInfo.Unnormalized().Path(),
+				SourceFilenameOrPath: meta.Filename,
 			})
 			if err != nil {
 				return true, err
diff --git a/resources/resource_metadata.go b/resources/resource_metadata.go
index 7d2459225..8861ded5c 100644
--- a/resources/resource_metadata.go
+++ b/resources/resource_metadata.go
@@ -15,6 +15,7 @@ package resources
 
 import (
 	"fmt"
+	"path/filepath"
 	"strconv"
 	"strings"
 
@@ -26,6 +27,7 @@ import (
 	"github.com/spf13/cast"
 
 	"github.com/gohugoio/hugo/common/maps"
+	"github.com/gohugoio/hugo/common/paths"
 )
 
 var (
@@ -172,6 +174,8 @@ func assignMetadata(metadata []map[string]any, ma *metaResource) error {
 				name, found := meta["name"]
 				if found {
 					name := cast.ToString(name)
+					// Bundled resources in sub folders are relative paths with forward slashes. Make sure any renames also matches that format:
+					name = paths.TrimLeading(filepath.ToSlash(name))
 					if !nameCounterFound {
 						nameCounterFound = strings.Contains(name, counterPlaceHolder)
 					}
diff --git a/resources/resource_test.go b/resources/resource_test.go
index ccce8eff7..d07770456 100644
--- a/resources/resource_test.go
+++ b/resources/resource_test.go
@@ -16,8 +16,26 @@ package resources
 import (
 	"os"
 	"testing"
+
+	qt "github.com/frankban/quicktest"
 )
 
+func TestAtomicStaler(t *testing.T) {
+	c := qt.New(t)
+
+	type test struct {
+		AtomicStaler
+	}
+
+	var v test
+
+	c.Assert(v.StaleVersion(), qt.Equals, uint32(0))
+	v.MarkStale()
+	c.Assert(v.StaleVersion(), qt.Equals, uint32(1))
+	v.MarkStale()
+	c.Assert(v.StaleVersion(), qt.Equals, uint32(2))
+}
+
 func BenchmarkHashImage(b *testing.B) {
 	f, err := os.Open("testdata/sunset.jpg")
 	if err != nil {
diff --git a/resources/resource_transformers/js/build.go b/resources/resource_transformers/js/build.go
index cc68d2253..bd943461f 100644
--- a/resources/resource_transformers/js/build.go
+++ b/resources/resource_transformers/js/build.go
@@ -1,4 +1,4 @@
-// Copyright 2020 The Hugo Authors. All rights reserved.
+// Copyright 2024 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -14,209 +14,69 @@
 package js
 
 import (
-	"errors"
-	"fmt"
-	"io"
-	"os"
 	"path"
-	"path/filepath"
 	"regexp"
-	"strings"
-
-	"github.com/spf13/afero"
-
-	"github.com/gohugoio/hugo/hugofs"
-	"github.com/gohugoio/hugo/media"
-
-	"github.com/gohugoio/hugo/common/herrors"
-	"github.com/gohugoio/hugo/common/text"
 
+	"github.com/evanw/esbuild/pkg/api"
 	"github.com/gohugoio/hugo/hugolib/filesystems"
-	"github.com/gohugoio/hugo/resources/internal"
+	"github.com/gohugoio/hugo/internal/js/esbuild"
 
-	"github.com/evanw/esbuild/pkg/api"
 	"github.com/gohugoio/hugo/resources"
 	"github.com/gohugoio/hugo/resources/resource"
 )
 
 // Client context for ESBuild.
 type Client struct {
-	rs  *resources.Spec
-	sfs *filesystems.SourceFilesystem
+	c *esbuild.BuildClient
 }
 
 // New creates a new client context.
 func New(fs *filesystems.SourceFilesystem, rs *resources.Spec) *Client {
 	return &Client{
-		rs:  rs,
-		sfs: fs,
+		c: esbuild.NewBuildClient(fs, rs),
 	}
 }
 
-type buildTransformation struct {
-	optsm map[string]any
-	c     *Client
-}
-
-func (t *buildTransformation) Key() internal.ResourceTransformationKey {
-	return internal.NewResourceTransformationKey("jsbuild", t.optsm)
+// Process processes a resource with the user provided options.
+func (c *Client) Process(res resources.ResourceTransformer, opts map[string]any) (resource.Resource, error) {
+	return res.Transform(
+		&buildTransformation{c: c, optsm: opts},
+	)
 }
 
-func (t *buildTransformation) Transform(ctx *resources.ResourceTransformationCtx) error {
-	ctx.OutMediaType = media.Builtin.JavascriptType
-
-	opts, err := decodeOptions(t.optsm)
-	if err != nil {
-		return err
+func (c *Client) transform(opts esbuild.Options, transformCtx *resources.ResourceTransformationCtx) (api.BuildResult, error) {
+	if transformCtx.DependencyManager != nil {
+		opts.DependencyManager = transformCtx.DependencyManager
 	}
 
-	if opts.TargetPath != "" {
-		ctx.OutPath = opts.TargetPath
-	} else {
-		ctx.ReplaceOutPathExtension(".js")
-	}
+	opts.StdinSourcePath = transformCtx.SourcePath
 
-	src, err := io.ReadAll(ctx.From)
+	result, err := c.c.Build(opts)
 	if err != nil {
-		return err
+		return result, err
 	}
 
-	opts.sourceDir = filepath.FromSlash(path.Dir(ctx.SourcePath))
-	opts.resolveDir = t.c.rs.Cfg.BaseConfig().WorkingDir // where node_modules gets resolved
-	opts.contents = string(src)
-	opts.mediaType = ctx.InMediaType
-	opts.tsConfig = t.c.rs.ResolveJSConfigFile("tsconfig.json")
-
-	buildOptions, err := toBuildOptions(opts)
-	if err != nil {
-		return err
-	}
-
-	buildOptions.Plugins, err = createBuildPlugins(ctx.DependencyManager, t.c, opts)
-	if err != nil {
-		return err
-	}
-
-	if buildOptions.Sourcemap == api.SourceMapExternal && buildOptions.Outdir == "" {
-		buildOptions.Outdir, err = os.MkdirTemp(os.TempDir(), "compileOutput")
-		if err != nil {
-			return err
-		}
-		defer os.Remove(buildOptions.Outdir)
-	}
-
-	if opts.Inject != nil {
-		// Resolve the absolute filenames.
-		for i, ext := range opts.Inject {
-			impPath := filepath.FromSlash(ext)
-			if filepath.IsAbs(impPath) {
-				return fmt.Errorf("inject: absolute paths not supported, must be relative to /assets")
-			}
-
-			m := resolveComponentInAssets(t.c.rs.Assets.Fs, impPath)
-
-			if m == nil {
-				return fmt.Errorf("inject: file %q not found", ext)
-			}
-
-			opts.Inject[i] = m.Filename
-
-		}
-
-		buildOptions.Inject = opts.Inject
-
-	}
-
-	result := api.Build(buildOptions)
-
-	if len(result.Errors) > 0 {
-
-		createErr := func(msg api.Message) error {
-			loc := msg.Location
-			if loc == nil {
-				return errors.New(msg.Text)
-			}
-			path := loc.File
-			if path == stdinImporter {
-				path = ctx.SourcePath
-			}
-
-			errorMessage := msg.Text
-			errorMessage = strings.ReplaceAll(errorMessage, nsImportHugo+":", "")
-
-			var (
-				f   afero.File
-				err error
-			)
-
-			if strings.HasPrefix(path, nsImportHugo) {
-				path = strings.TrimPrefix(path, nsImportHugo+":")
-				f, err = hugofs.Os.Open(path)
-			} else {
-				var fi os.FileInfo
-				fi, err = t.c.sfs.Fs.Stat(path)
-				if err == nil {
-					m := fi.(hugofs.FileMetaInfo).Meta()
-					path = m.Filename
-					f, err = m.Open()
-				}
-
-			}
-
-			if err == nil {
-				fe := herrors.
-					NewFileErrorFromName(errors.New(errorMessage), path).
-					UpdatePosition(text.Position{Offset: -1, LineNumber: loc.Line, ColumnNumber: loc.Column}).
-					UpdateContent(f, nil)
-
-				f.Close()
-				return fe
-			}
-
-			return fmt.Errorf("%s", errorMessage)
-		}
-
-		var errors []error
-
-		for _, msg := range result.Errors {
-			errors = append(errors, createErr(msg))
-		}
-
-		// Return 1, log the rest.
-		for i, err := range errors {
-			if i > 0 {
-				t.c.rs.Logger.Errorf("js.Build failed: %s", err)
-			}
-		}
-
-		return errors[0]
-	}
-
-	if buildOptions.Sourcemap == api.SourceMapExternal {
+	if opts.ExternalOptions.SourceMap == "linked" || opts.ExternalOptions.SourceMap == "external" {
 		content := string(result.OutputFiles[1].Contents)
-		symPath := path.Base(ctx.OutPath) + ".map"
-		re := regexp.MustCompile(`//# sourceMappingURL=.*\n?`)
-		content = re.ReplaceAllString(content, "//# sourceMappingURL="+symPath+"\n")
+		if opts.ExternalOptions.SourceMap == "linked" {
+			symPath := path.Base(transformCtx.OutPath) + ".map"
+			re := regexp.MustCompile(`//# sourceMappingURL=.*\n?`)
+			content = re.ReplaceAllString(content, "//# sourceMappingURL="+symPath+"\n")
+		}
 
-		if err = ctx.PublishSourceMap(string(result.OutputFiles[0].Contents)); err != nil {
-			return err
+		if err = transformCtx.PublishSourceMap(string(result.OutputFiles[0].Contents)); err != nil {
+			return result, err
 		}
-		_, err := ctx.To.Write([]byte(content))
+		_, err := transformCtx.To.Write([]byte(content))
 		if err != nil {
-			return err
+			return result, err
 		}
 	} else {
-		_, err := ctx.To.Write(result.OutputFiles[0].Contents)
+		_, err := transformCtx.To.Write(result.OutputFiles[0].Contents)
 		if err != nil {
-			return err
+			return result, err
 		}
-	}
-	return nil
-}
 
-// Process process esbuild transform
-func (c *Client) Process(res resources.ResourceTransformer, opts map[string]any) (resource.Resource, error) {
-	return res.Transform(
-		&buildTransformation{c: c, optsm: opts},
-	)
+	}
+	return result, nil
 }
diff --git a/resources/resource_transformers/js/js_integration_test.go b/resources/resource_transformers/js/js_integration_test.go
index 304c51d33..c62312ef5 100644
--- a/resources/resource_transformers/js/js_integration_test.go
+++ b/resources/resource_transformers/js/js_integration_test.go
@@ -1,4 +1,4 @@
-// Copyright 2021 The Hugo Authors. All rights reserved.
+// Copyright 2024 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -14,13 +14,16 @@
 package js_test
 
 import (
+	"os"
 	"path/filepath"
 	"strings"
 	"testing"
 
 	qt "github.com/frankban/quicktest"
+	"github.com/gohugoio/hugo/common/paths"
 	"github.com/gohugoio/hugo/htesting"
 	"github.com/gohugoio/hugo/hugolib"
+	"github.com/gohugoio/hugo/internal/js/esbuild"
 )
 
 func TestBuildVariants(t *testing.T) {
@@ -173,7 +176,7 @@ hello:
 hello:
    other: "Bonjour"
 -- layouts/index.html --
-{{ $options := dict "minify" false "externals" (slice "react" "react-dom") }}
+{{ $options := dict "minify" false "externals" (slice "react" "react-dom")  "sourcemap" "linked" }}
 {{ $js := resources.Get "js/main.js" | js.Build $options }}
 JS:  {{ template "print" $js }}
 {{ $jsx := resources.Get "js/myjsx.jsx" | js.Build $options }}
@@ -201,14 +204,31 @@ TS2: {{ template "print" $ts2 }}
 			TxtarString:     files,
 		}).Build()
 
-	b.AssertFileContent("public/js/myts.js", `//# sourceMappingURL=data:application/json;base64,ewogICJ2ZXJz`)
-	b.AssertFileContent("public/js/myts2.js.map", `"version": 3,`)
+	b.AssertFileContent("public/js/main.js", `//# sourceMappingURL=main.js.map`)
+	b.AssertFileContent("public/js/main.js.map", `"version":3`, "! ns-hugo")                                   // linked
+	b.AssertFileContent("public/js/myts.js", `//# sourceMappingURL=data:application/json;base64,ewogICJ2ZXJz`) // inline
 	b.AssertFileContent("public/index.html", `
 		console.log(&#34;included&#34;);
 		if (hasSpace.test(string))
 		var React = __toESM(__require(&#34;react&#34;));
 		function greeter(person) {
 `)
+
+	checkMap := func(p string, expectLen int) {
+		s := b.FileContent(p)
+		sources := esbuild.SourcesFromSourceMap(s)
+		b.Assert(sources, qt.HasLen, expectLen)
+
+		// Check that all source files exist.
+		for _, src := range sources {
+			filename, ok := paths.UrlStringToFilename(src)
+			b.Assert(ok, qt.IsTrue)
+			_, err := os.Stat(filename)
+			b.Assert(err, qt.IsNil, qt.Commentf("src: %q", src))
+		}
+	}
+
+	checkMap("public/js/main.js.map", 4)
 }
 
 func TestBuildError(t *testing.T) {
diff --git a/resources/resource_transformers/js/options.go b/resources/resource_transformers/js/options.go
deleted file mode 100644
index 8c271d032..000000000
--- a/resources/resource_transformers/js/options.go
+++ /dev/null
@@ -1,461 +0,0 @@
-// Copyright 2020 The Hugo Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package js
-
-import (
-	"encoding/json"
-	"fmt"
-	"os"
-	"path/filepath"
-	"strings"
-
-	"github.com/gohugoio/hugo/common/maps"
-	"github.com/gohugoio/hugo/common/paths"
-	"github.com/gohugoio/hugo/identity"
-	"github.com/spf13/afero"
-
-	"github.com/evanw/esbuild/pkg/api"
-
-	"github.com/gohugoio/hugo/hugofs"
-	"github.com/gohugoio/hugo/media"
-	"github.com/mitchellh/mapstructure"
-)
-
-const (
-	nsImportHugo = "ns-hugo"
-	nsParams     = "ns-params"
-
-	stdinImporter = "<stdin>"
-)
-
-// Options esbuild configuration
-type Options struct {
-	// If not set, the source path will be used as the base target path.
-	// Note that the target path's extension may change if the target MIME type
-	// is different, e.g. when the source is TypeScript.
-	TargetPath string
-
-	// Whether to minify to output.
-	Minify bool
-
-	// Whether to write mapfiles
-	SourceMap string
-
-	// The language target.
-	// One of: es2015, es2016, es2017, es2018, es2019, es2020 or esnext.
-	// Default is esnext.
-	Target string
-
-	// The output format.
-	// One of: iife, cjs, esm
-	// Default is to esm.
-	Format string
-
-	// External dependencies, e.g. "react".
-	Externals []string
-
-	// This option allows you to automatically replace a global variable with an import from another file.
-	// The filenames must be relative to /assets.
-	// See https://esbuild.github.io/api/#inject
-	Inject []string
-
-	// User defined symbols.
-	Defines map[string]any
-
-	// Maps a component import to another.
-	Shims map[string]string
-
-	// User defined params. Will be marshaled to JSON and available as "@params", e.g.
-	//     import * as params from '@params';
-	Params any
-
-	// What to use instead of React.createElement.
-	JSXFactory string
-
-	// What to use instead of React.Fragment.
-	JSXFragment string
-
-	// What to do about JSX syntax.
-	// See https://esbuild.github.io/api/#jsx
-	JSX string
-
-	// Which library to use to automatically import JSX helper functions from. Only works if JSX is set to automatic.
-	// See https://esbuild.github.io/api/#jsx-import-source
-	JSXImportSource string
-
-	// There is/was a bug in WebKit with severe performance issue with the tracking
-	// of TDZ checks in JavaScriptCore.
-	//
-	// Enabling this flag removes the TDZ and `const` assignment checks and
-	// may improve performance of larger JS codebases until the WebKit fix
-	// is in widespread use.
-	//
-	// See https://bugs.webkit.org/show_bug.cgi?id=199866
-	// Deprecated: This no longer have any effect and will be removed.
-	// TODO(bep) remove. See https://github.com/evanw/esbuild/commit/869e8117b499ca1dbfc5b3021938a53ffe934dba
-	AvoidTDZ bool
-
-	mediaType  media.Type
-	outDir     string
-	contents   string
-	sourceDir  string
-	resolveDir string
-	tsConfig   string
-}
-
-func decodeOptions(m map[string]any) (Options, error) {
-	var opts Options
-
-	if err := mapstructure.WeakDecode(m, &opts); err != nil {
-		return opts, err
-	}
-
-	if opts.TargetPath != "" {
-		opts.TargetPath = paths.ToSlashTrimLeading(opts.TargetPath)
-	}
-
-	opts.Target = strings.ToLower(opts.Target)
-	opts.Format = strings.ToLower(opts.Format)
-
-	return opts, nil
-}
-
-var extensionToLoaderMap = map[string]api.Loader{
-	".js":   api.LoaderJS,
-	".mjs":  api.LoaderJS,
-	".cjs":  api.LoaderJS,
-	".jsx":  api.LoaderJSX,
-	".ts":   api.LoaderTS,
-	".tsx":  api.LoaderTSX,
-	".css":  api.LoaderCSS,
-	".json": api.LoaderJSON,
-	".txt":  api.LoaderText,
-}
-
-func loaderFromFilename(filename string) api.Loader {
-	l, found := extensionToLoaderMap[filepath.Ext(filename)]
-	if found {
-		return l
-	}
-	return api.LoaderJS
-}
-
-func resolveComponentInAssets(fs afero.Fs, impPath string) *hugofs.FileMeta {
-	findFirst := func(base string) *hugofs.FileMeta {
-		// This is the most common sub-set of ESBuild's default extensions.
-		// We assume that imports of JSON, CSS etc. will be using their full
-		// name with extension.
-		for _, ext := range []string{".js", ".ts", ".tsx", ".jsx"} {
-			if strings.HasSuffix(impPath, ext) {
-				// Import of foo.js.js need the full name.
-				continue
-			}
-			if fi, err := fs.Stat(base + ext); err == nil {
-				return fi.(hugofs.FileMetaInfo).Meta()
-			}
-		}
-
-		// Not found.
-		return nil
-	}
-
-	var m *hugofs.FileMeta
-
-	// We need to check if this is a regular file imported without an extension.
-	// There may be ambiguous situations where both foo.js and foo/index.js exists.
-	// This import order is in line with both how Node and ESBuild's native
-	// import resolver works.
-
-	// It may be a regular file imported without an extension, e.g.
-	// foo or foo/index.
-	m = findFirst(impPath)
-	if m != nil {
-		return m
-	}
-
-	base := filepath.Base(impPath)
-	if base == "index" {
-		// try index.esm.js etc.
-		m = findFirst(impPath + ".esm")
-		if m != nil {
-			return m
-		}
-	}
-
-	// Check the path as is.
-	fi, err := fs.Stat(impPath)
-
-	if err == nil {
-		if fi.IsDir() {
-			m = findFirst(filepath.Join(impPath, "index"))
-			if m == nil {
-				m = findFirst(filepath.Join(impPath, "index.esm"))
-			}
-		} else {
-			m = fi.(hugofs.FileMetaInfo).Meta()
-		}
-	} else if strings.HasSuffix(base, ".js") {
-		m = findFirst(strings.TrimSuffix(impPath, ".js"))
-	}
-
-	return m
-}
-
-func createBuildPlugins(depsManager identity.Manager, c *Client, opts Options) ([]api.Plugin, error) {
-	fs := c.rs.Assets
-
-	resolveImport := func(args api.OnResolveArgs) (api.OnResolveResult, error) {
-		impPath := args.Path
-		if opts.Shims != nil {
-			override, found := opts.Shims[impPath]
-			if found {
-				impPath = override
-			}
-		}
-		isStdin := args.Importer == stdinImporter
-		var relDir string
-		if !isStdin {
-			rel, found := fs.MakePathRelative(args.Importer, true)
-			if !found {
-				// Not in any of the /assets folders.
-				// This is an import from a node_modules, let
-				// ESBuild resolve this.
-				return api.OnResolveResult{}, nil
-			}
-
-			relDir = filepath.Dir(rel)
-		} else {
-			relDir = opts.sourceDir
-		}
-
-		// Imports not starting with a "." is assumed to live relative to /assets.
-		// Hugo makes no assumptions about the directory structure below /assets.
-		if relDir != "" && strings.HasPrefix(impPath, ".") {
-			impPath = filepath.Join(relDir, impPath)
-		}
-
-		m := resolveComponentInAssets(fs.Fs, impPath)
-
-		if m != nil {
-			depsManager.AddIdentity(m.PathInfo)
-
-			// Store the source root so we can create a jsconfig.json
-			// to help IntelliSense when the build is done.
-			// This should be a small number of elements, and when
-			// in server mode, we may get stale entries on renames etc.,
-			// but that shouldn't matter too much.
-			c.rs.JSConfigBuilder.AddSourceRoot(m.SourceRoot)
-			return api.OnResolveResult{Path: m.Filename, Namespace: nsImportHugo}, nil
-		}
-
-		// Fall back to ESBuild's resolve.
-		return api.OnResolveResult{}, nil
-	}
-
-	importResolver := api.Plugin{
-		Name: "hugo-import-resolver",
-		Setup: func(build api.PluginBuild) {
-			build.OnResolve(api.OnResolveOptions{Filter: `.*`},
-				func(args api.OnResolveArgs) (api.OnResolveResult, error) {
-					return resolveImport(args)
-				})
-			build.OnLoad(api.OnLoadOptions{Filter: `.*`, Namespace: nsImportHugo},
-				func(args api.OnLoadArgs) (api.OnLoadResult, error) {
-					b, err := os.ReadFile(args.Path)
-					if err != nil {
-						return api.OnLoadResult{}, fmt.Errorf("failed to read %q: %w", args.Path, err)
-					}
-					c := string(b)
-					return api.OnLoadResult{
-						// See https://github.com/evanw/esbuild/issues/502
-						// This allows all modules to resolve dependencies
-						// in the main project's node_modules.
-						ResolveDir: opts.resolveDir,
-						Contents:   &c,
-						Loader:     loaderFromFilename(args.Path),
-					}, nil
-				})
-		},
-	}
-
-	params := opts.Params
-	if params == nil {
-		// This way @params will always resolve to something.
-		params = make(map[string]any)
-	}
-
-	b, err := json.Marshal(params)
-	if err != nil {
-		return nil, fmt.Errorf("failed to marshal params: %w", err)
-	}
-	bs := string(b)
-	paramsPlugin := api.Plugin{
-		Name: "hugo-params-plugin",
-		Setup: func(build api.PluginBuild) {
-			build.OnResolve(api.OnResolveOptions{Filter: `^@params$`},
-				func(args api.OnResolveArgs) (api.OnResolveResult, error) {
-					return api.OnResolveResult{
-						Path:      args.Path,
-						Namespace: nsParams,
-					}, nil
-				})
-			build.OnLoad(api.OnLoadOptions{Filter: `.*`, Namespace: nsParams},
-				func(args api.OnLoadArgs) (api.OnLoadResult, error) {
-					return api.OnLoadResult{
-						Contents: &bs,
-						Loader:   api.LoaderJSON,
-					}, nil
-				})
-		},
-	}
-
-	return []api.Plugin{importResolver, paramsPlugin}, nil
-}
-
-func toBuildOptions(opts Options) (buildOptions api.BuildOptions, err error) {
-	var target api.Target
-	switch opts.Target {
-	case "", "esnext":
-		target = api.ESNext
-	case "es5":
-		target = api.ES5
-	case "es6", "es2015":
-		target = api.ES2015
-	case "es2016":
-		target = api.ES2016
-	case "es2017":
-		target = api.ES2017
-	case "es2018":
-		target = api.ES2018
-	case "es2019":
-		target = api.ES2019
-	case "es2020":
-		target = api.ES2020
-	case "es2021":
-		target = api.ES2021
-	case "es2022":
-		target = api.ES2022
-	case "es2023":
-		target = api.ES2023
-	default:
-		err = fmt.Errorf("invalid target: %q", opts.Target)
-		return
-	}
-
-	mediaType := opts.mediaType
-	if mediaType.IsZero() {
-		mediaType = media.Builtin.JavascriptType
-	}
-
-	var loader api.Loader
-	switch mediaType.SubType {
-	// TODO(bep) ESBuild support a set of other loaders, but I currently fail
-	// to see the relevance. That may change as we start using this.
-	case media.Builtin.JavascriptType.SubType:
-		loader = api.LoaderJS
-	case media.Builtin.TypeScriptType.SubType:
-		loader = api.LoaderTS
-	case media.Builtin.TSXType.SubType:
-		loader = api.LoaderTSX
-	case media.Builtin.JSXType.SubType:
-		loader = api.LoaderJSX
-	default:
-		err = fmt.Errorf("unsupported Media Type: %q", opts.mediaType)
-		return
-	}
-
-	var format api.Format
-	// One of: iife, cjs, esm
-	switch opts.Format {
-	case "", "iife":
-		format = api.FormatIIFE
-	case "esm":
-		format = api.FormatESModule
-	case "cjs":
-		format = api.FormatCommonJS
-	default:
-		err = fmt.Errorf("unsupported script output format: %q", opts.Format)
-		return
-	}
-
-	var jsx api.JSX
-	switch opts.JSX {
-	case "", "transform":
-		jsx = api.JSXTransform
-	case "preserve":
-		jsx = api.JSXPreserve
-	case "automatic":
-		jsx = api.JSXAutomatic
-	default:
-		err = fmt.Errorf("unsupported jsx type: %q", opts.JSX)
-		return
-	}
-
-	var defines map[string]string
-	if opts.Defines != nil {
-		defines = maps.ToStringMapString(opts.Defines)
-	}
-
-	// By default we only need to specify outDir and no outFile
-	outDir := opts.outDir
-	outFile := ""
-	var sourceMap api.SourceMap
-	switch opts.SourceMap {
-	case "inline":
-		sourceMap = api.SourceMapInline
-	case "external":
-		sourceMap = api.SourceMapExternal
-	case "":
-		sourceMap = api.SourceMapNone
-	default:
-		err = fmt.Errorf("unsupported sourcemap type: %q", opts.SourceMap)
-		return
-	}
-
-	buildOptions = api.BuildOptions{
-		Outfile: outFile,
-		Bundle:  true,
-
-		Target:    target,
-		Format:    format,
-		Sourcemap: sourceMap,
-
-		MinifyWhitespace:  opts.Minify,
-		MinifyIdentifiers: opts.Minify,
-		MinifySyntax:      opts.Minify,
-
-		Outdir: outDir,
-		Define: defines,
-
-		External: opts.Externals,
-
-		JSXFactory:  opts.JSXFactory,
-		JSXFragment: opts.JSXFragment,
-
-		JSX:             jsx,
-		JSXImportSource: opts.JSXImportSource,
-
-		Tsconfig: opts.tsConfig,
-
-		// Note: We're not passing Sourcefile to ESBuild.
-		// This makes ESBuild pass `stdin` as the Importer to the import
-		// resolver, which is what we need/expect.
-		Stdin: &api.StdinOptions{
-			Contents:   opts.contents,
-			ResolveDir: opts.resolveDir,
-			Loader:     loader,
-		},
-	}
-	return
-}
diff --git a/resources/resource_transformers/js/options_test.go b/resources/resource_transformers/js/options_test.go
deleted file mode 100644
index 53aa9b6bb..000000000
--- a/resources/resource_transformers/js/options_test.go
+++ /dev/null
@@ -1,241 +0,0 @@
-// Copyright 2020 The Hugo Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package js
-
-import (
-	"path"
-	"path/filepath"
-	"testing"
-
-	"github.com/gohugoio/hugo/config"
-	"github.com/gohugoio/hugo/config/testconfig"
-	"github.com/gohugoio/hugo/hugofs"
-	"github.com/gohugoio/hugo/hugolib/filesystems"
-	"github.com/gohugoio/hugo/hugolib/paths"
-	"github.com/gohugoio/hugo/media"
-
-	"github.com/spf13/afero"
-
-	"github.com/evanw/esbuild/pkg/api"
-
-	qt "github.com/frankban/quicktest"
-)
-
-// This test is added to test/warn against breaking the "stability" of the
-// cache key. It's sometimes needed to break this, but should be avoided if possible.
-func TestOptionKey(t *testing.T) {
-	c := qt.New(t)
-
-	opts := map[string]any{
-		"TargetPath": "foo",
-		"Target":     "es2018",
-	}
-
-	key := (&buildTransformation{optsm: opts}).Key()
-
-	c.Assert(key.Value(), qt.Equals, "jsbuild_1533819657654811600")
-}
-
-func TestToBuildOptions(t *testing.T) {
-	c := qt.New(t)
-
-	opts, err := toBuildOptions(Options{mediaType: media.Builtin.JavascriptType})
-
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle: true,
-		Target: api.ESNext,
-		Format: api.FormatIIFE,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-	})
-
-	opts, err = toBuildOptions(Options{
-		Target:    "es2018",
-		Format:    "cjs",
-		Minify:    true,
-		mediaType: media.Builtin.JavascriptType,
-		AvoidTDZ:  true,
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle:            true,
-		Target:            api.ES2018,
-		Format:            api.FormatCommonJS,
-		MinifyIdentifiers: true,
-		MinifySyntax:      true,
-		MinifyWhitespace:  true,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-	})
-
-	opts, err = toBuildOptions(Options{
-		Target: "es2018", Format: "cjs", Minify: true, mediaType: media.Builtin.JavascriptType,
-		SourceMap: "inline",
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle:            true,
-		Target:            api.ES2018,
-		Format:            api.FormatCommonJS,
-		MinifyIdentifiers: true,
-		MinifySyntax:      true,
-		MinifyWhitespace:  true,
-		Sourcemap:         api.SourceMapInline,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-	})
-
-	opts, err = toBuildOptions(Options{
-		Target: "es2018", Format: "cjs", Minify: true, mediaType: media.Builtin.JavascriptType,
-		SourceMap: "inline",
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle:            true,
-		Target:            api.ES2018,
-		Format:            api.FormatCommonJS,
-		MinifyIdentifiers: true,
-		MinifySyntax:      true,
-		MinifyWhitespace:  true,
-		Sourcemap:         api.SourceMapInline,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-	})
-
-	opts, err = toBuildOptions(Options{
-		Target: "es2018", Format: "cjs", Minify: true, mediaType: media.Builtin.JavascriptType,
-		SourceMap: "external",
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle:            true,
-		Target:            api.ES2018,
-		Format:            api.FormatCommonJS,
-		MinifyIdentifiers: true,
-		MinifySyntax:      true,
-		MinifyWhitespace:  true,
-		Sourcemap:         api.SourceMapExternal,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-	})
-
-	opts, err = toBuildOptions(Options{
-		mediaType: media.Builtin.JavascriptType,
-		JSX:       "automatic", JSXImportSource: "preact",
-	})
-	c.Assert(err, qt.IsNil)
-	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
-		Bundle: true,
-		Target: api.ESNext,
-		Format: api.FormatIIFE,
-		Stdin: &api.StdinOptions{
-			Loader: api.LoaderJS,
-		},
-		JSX:             api.JSXAutomatic,
-		JSXImportSource: "preact",
-	})
-}
-
-func TestToBuildOptionsTarget(t *testing.T) {
-	c := qt.New(t)
-
-	for _, test := range []struct {
-		target string
-		expect api.Target
-	}{
-		{"es2015", api.ES2015},
-		{"es2016", api.ES2016},
-		{"es2017", api.ES2017},
-		{"es2018", api.ES2018},
-		{"es2019", api.ES2019},
-		{"es2020", api.ES2020},
-		{"es2021", api.ES2021},
-		{"es2022", api.ES2022},
-		{"es2023", api.ES2023},
-		{"", api.ESNext},
-		{"esnext", api.ESNext},
-	} {
-		c.Run(test.target, func(c *qt.C) {
-			opts, err := toBuildOptions(Options{
-				Target:    test.target,
-				mediaType: media.Builtin.JavascriptType,
-			})
-			c.Assert(err, qt.IsNil)
-			c.Assert(opts.Target, qt.Equals, test.expect)
-		})
-	}
-}
-
-func TestResolveComponentInAssets(t *testing.T) {
-	c := qt.New(t)
-
-	for _, test := range []struct {
-		name    string
-		files   []string
-		impPath string
-		expect  string
-	}{
-		{"Basic, extension", []string{"foo.js", "bar.js"}, "foo.js", "foo.js"},
-		{"Basic, no extension", []string{"foo.js", "bar.js"}, "foo", "foo.js"},
-		{"Basic, no extension, typescript", []string{"foo.ts", "bar.js"}, "foo", "foo.ts"},
-		{"Not found", []string{"foo.js", "bar.js"}, "moo.js", ""},
-		{"Not found, double js extension", []string{"foo.js.js", "bar.js"}, "foo.js", ""},
-		{"Index file, folder only", []string{"foo/index.js", "bar.js"}, "foo", "foo/index.js"},
-		{"Index file, folder and index", []string{"foo/index.js", "bar.js"}, "foo/index", "foo/index.js"},
-		{"Index file, folder and index and suffix", []string{"foo/index.js", "bar.js"}, "foo/index.js", "foo/index.js"},
-		{"Index ESM file, folder only", []string{"foo/index.esm.js", "bar.js"}, "foo", "foo/index.esm.js"},
-		{"Index ESM file, folder and index", []string{"foo/index.esm.js", "bar.js"}, "foo/index", "foo/index.esm.js"},
-		{"Index ESM file, folder and index and suffix", []string{"foo/index.esm.js", "bar.js"}, "foo/index.esm.js", "foo/index.esm.js"},
-		// We added these index.esm.js cases in v0.101.0. The case below is unlikely to happen in the wild, but add a test
-		// to document Hugo's behavior. We pick the file with the name index.js; anything else would be breaking.
-		{"Index and Index ESM file, folder only", []string{"foo/index.esm.js", "foo/index.js", "bar.js"}, "foo", "foo/index.js"},
-
-		// Issue #8949
-		{"Check file before directory", []string{"foo.js", "foo/index.js"}, "foo", "foo.js"},
-	} {
-		c.Run(test.name, func(c *qt.C) {
-			baseDir := "assets"
-			mfs := afero.NewMemMapFs()
-
-			for _, filename := range test.files {
-				c.Assert(afero.WriteFile(mfs, filepath.Join(baseDir, filename), []byte("let foo='bar';"), 0o777), qt.IsNil)
-			}
-
-			conf := testconfig.GetTestConfig(mfs, config.New())
-			fs := hugofs.NewFrom(mfs, conf.BaseConfig())
-
-			p, err := paths.New(fs, conf)
-			c.Assert(err, qt.IsNil)
-			bfs, err := filesystems.NewBase(p, nil)
-			c.Assert(err, qt.IsNil)
-
-			got := resolveComponentInAssets(bfs.Assets.Fs, test.impPath)
-
-			gotPath := ""
-			expect := test.expect
-			if got != nil {
-				gotPath = filepath.ToSlash(got.Filename)
-				expect = path.Join(baseDir, test.expect)
-			}
-
-			c.Assert(gotPath, qt.Equals, expect)
-		})
-	}
-}
diff --git a/resources/resource_transformers/js/transform.go b/resources/resource_transformers/js/transform.go
new file mode 100644
index 000000000..13909e54c
--- /dev/null
+++ b/resources/resource_transformers/js/transform.go
@@ -0,0 +1,68 @@
+// Copyright 2024 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package js
+
+import (
+	"io"
+	"path"
+	"path/filepath"
+
+	"github.com/gohugoio/hugo/internal/js/esbuild"
+	"github.com/gohugoio/hugo/media"
+	"github.com/gohugoio/hugo/resources"
+	"github.com/gohugoio/hugo/resources/internal"
+)
+
+type buildTransformation struct {
+	optsm map[string]any
+	c     *Client
+}
+
+func (t *buildTransformation) Key() internal.ResourceTransformationKey {
+	return internal.NewResourceTransformationKey("jsbuild", t.optsm)
+}
+
+func (t *buildTransformation) Transform(ctx *resources.ResourceTransformationCtx) error {
+	ctx.OutMediaType = media.Builtin.JavascriptType
+
+	var opts esbuild.Options
+
+	if t.optsm != nil {
+		optsExt, err := esbuild.DecodeExternalOptions(t.optsm)
+		if err != nil {
+			return err
+		}
+		opts.ExternalOptions = optsExt
+	}
+
+	if opts.TargetPath != "" {
+		ctx.OutPath = opts.TargetPath
+	} else {
+		ctx.ReplaceOutPathExtension(".js")
+	}
+
+	src, err := io.ReadAll(ctx.From)
+	if err != nil {
+		return err
+	}
+
+	opts.SourceDir = filepath.FromSlash(path.Dir(ctx.SourcePath))
+	opts.Contents = string(src)
+	opts.MediaType = ctx.InMediaType
+	opts.Stdin = true
+
+	_, err = t.c.transform(opts, ctx)
+
+	return err
+}
diff --git a/resources/resource_transformers/tocss/dartsass/transform.go b/resources/resource_transformers/tocss/dartsass/transform.go
index 0d7b57062..77bacc115 100644
--- a/resources/resource_transformers/tocss/dartsass/transform.go
+++ b/resources/resource_transformers/tocss/dartsass/transform.go
@@ -139,7 +139,7 @@ func (t importResolver) CanonicalizeURL(url string) (string, error) {
 		return url, nil
 	}
 
-	filePath, isURL := paths.UrlToFilename(url)
+	filePath, isURL := paths.UrlStringToFilename(url)
 	var prevDir string
 	var pathDir string
 	if isURL {
@@ -195,7 +195,7 @@ func (t importResolver) Load(url string) (godartsass.Import, error) {
 	if url == sass.HugoVarsNamespace {
 		return t.varsStylesheet, nil
 	}
-	filename, _ := paths.UrlToFilename(url)
+	filename, _ := paths.UrlStringToFilename(url)
 	b, err := afero.ReadFile(hugofs.Os, filename)
 
 	sourceSyntax := godartsass.SourceSyntaxSCSS
diff --git a/resources/transform.go b/resources/transform.go
index 336495e6d..4214067bd 100644
--- a/resources/transform.go
+++ b/resources/transform.go
@@ -52,6 +52,8 @@ var (
 	_ identity.IdentityGroupProvider     = (*resourceAdapterInner)(nil)
 	_ resource.Source                    = (*resourceAdapter)(nil)
 	_ resource.Identifier                = (*resourceAdapter)(nil)
+	_ targetPathProvider                 = (*resourceAdapter)(nil)
+	_ sourcePathProvider                 = (*resourceAdapter)(nil)
 	_ resource.ResourceNameTitleProvider = (*resourceAdapter)(nil)
 	_ resource.WithResourceMetaProvider  = (*resourceAdapter)(nil)
 	_ identity.DependencyManagerProvider = (*resourceAdapter)(nil)
@@ -277,6 +279,19 @@ func (r *resourceAdapter) Key() string {
 	return r.target.(resource.Identifier).Key()
 }
 
+func (r *resourceAdapter) targetPath() string {
+	r.init(false, false)
+	return r.target.(targetPathProvider).targetPath()
+}
+
+func (r *resourceAdapter) sourcePath() string {
+	r.init(false, false)
+	if sp, ok := r.target.(sourcePathProvider); ok {
+		return sp.sourcePath()
+	}
+	return ""
+}
+
 func (r *resourceAdapter) MediaType() media.Type {
 	r.init(false, false)
 	return r.target.MediaType()
diff --git a/tpl/debug/debug.go b/tpl/debug/debug.go
index ae1acf5eb..fd676f0e2 100644
--- a/tpl/debug/debug.go
+++ b/tpl/debug/debug.go
@@ -41,7 +41,7 @@ func New(d *deps.Deps) *Namespace {
 
 	l := d.Log.InfoCommand("timer")
 
-	d.BuildEndListeners.Add(func() {
+	d.BuildEndListeners.Add(func(...any) bool {
 		type data struct {
 			Name     string
 			Count    int
@@ -84,6 +84,8 @@ func New(d *deps.Deps) *Namespace {
 		}
 
 		ns.timers = make(map[string][]*timer)
+
+		return false
 	})
 
 	return ns
diff --git a/tpl/fmt/fmt.go b/tpl/fmt/fmt.go
index e9c18360a..264cb1435 100644
--- a/tpl/fmt/fmt.go
+++ b/tpl/fmt/fmt.go
@@ -30,8 +30,9 @@ func New(d *deps.Deps) *Namespace {
 		logger: d.Log,
 	}
 
-	d.BuildStartListeners.Add(func() {
+	d.BuildStartListeners.Add(func(...any) bool {
 		ns.logger.Reset()
+		return false
 	})
 
 	return ns
diff --git a/tpl/js/init.go b/tpl/js/init.go
index 69d7c7275..97e76c33d 100644
--- a/tpl/js/init.go
+++ b/tpl/js/init.go
@@ -24,7 +24,10 @@ const name = "js"
 
 func init() {
 	f := func(d *deps.Deps) *internal.TemplateFuncsNamespace {
-		ctx := New(d)
+		ctx, err := New(d)
+		if err != nil {
+			panic(err)
+		}
 
 		ns := &internal.TemplateFuncsNamespace{
 			Name:    name,
diff --git a/tpl/js/js.go b/tpl/js/js.go
index c68e0af92..b686b76a7 100644
--- a/tpl/js/js.go
+++ b/tpl/js/js.go
@@ -1,4 +1,4 @@
-// Copyright 2020 The Hugo Authors. All rights reserved.
+// Copyright 2024 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -17,29 +17,47 @@ package js
 import (
 	"errors"
 
+	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/deps"
+	"github.com/gohugoio/hugo/internal/js/esbuild"
 	"github.com/gohugoio/hugo/resources"
 	"github.com/gohugoio/hugo/resources/resource"
+	"github.com/gohugoio/hugo/resources/resource_factories/create"
 	"github.com/gohugoio/hugo/resources/resource_transformers/babel"
-	"github.com/gohugoio/hugo/resources/resource_transformers/js"
+	jstransform "github.com/gohugoio/hugo/resources/resource_transformers/js"
 	"github.com/gohugoio/hugo/tpl/internal/resourcehelpers"
 )
 
 // New returns a new instance of the js-namespaced template functions.
-func New(deps *deps.Deps) *Namespace {
-	if deps.ResourceSpec == nil {
-		return &Namespace{}
+func New(d *deps.Deps) (*Namespace, error) {
+	if d.ResourceSpec == nil {
+		return &Namespace{}, nil
 	}
-	return &Namespace{
-		client:      js.New(deps.BaseFs.Assets, deps.ResourceSpec),
-		babelClient: babel.New(deps.ResourceSpec),
+
+	batcherClient, err := esbuild.NewBatcherClient(d)
+	if err != nil {
+		return nil, err
 	}
+
+	return &Namespace{
+		d:                 d,
+		jsTransformClient: jstransform.New(d.BaseFs.Assets, d.ResourceSpec),
+		jsBatcherClient:   batcherClient,
+		jsBatcherStore:    maps.NewCache[string, esbuild.Batcher](),
+		createClient:      create.New(d.ResourceSpec),
+		babelClient:       babel.New(d.ResourceSpec),
+	}, nil
 }
 
 // Namespace provides template functions for the "js" namespace.
 type Namespace struct {
-	client      *js.Client
-	babelClient *babel.Client
+	d *deps.Deps
+
+	jsTransformClient *jstransform.Client
+	createClient      *create.Client
+	babelClient       *babel.Client
+	jsBatcherClient   *esbuild.BatcherClient
+	jsBatcherStore    *maps.Cache[string, esbuild.Batcher]
 }
 
 // Build processes the given Resource with ESBuild.
@@ -65,7 +83,24 @@ func (ns *Namespace) Build(args ...any) (resource.Resource, error) {
 		m = map[string]any{"targetPath": targetPath}
 	}
 
-	return ns.client.Process(r, m)
+	return ns.jsTransformClient.Process(r, m)
+}
+
+// Batch creates a new Batcher with the given ID.
+// Repeated calls with the same ID will return the same Batcher.
+// The ID will be used to name the root directory of the batch.
+// Forward slashes in the ID is allowed.
+func (ns *Namespace) Batch(id string) (esbuild.Batcher, error) {
+	if err := esbuild.ValidateBatchID(id, true); err != nil {
+		return nil, err
+	}
+	b, err := ns.jsBatcherStore.GetOrCreate(id, func() (esbuild.Batcher, error) {
+		return ns.jsBatcherClient.New(id)
+	})
+	if err != nil {
+		return nil, err
+	}
+	return b, nil
 }
 
 // Babel processes the given Resource with Babel.
diff --git a/tpl/partials/partials.go b/tpl/partials/partials.go
index 8de312fd8..4441b5fa5 100644
--- a/tpl/partials/partials.go
+++ b/tpl/partials/partials.go
@@ -81,8 +81,9 @@ func New(deps *deps.Deps) *Namespace {
 
 	cache := &partialCache{cache: lru}
 	deps.BuildStartListeners.Add(
-		func() {
+		func(...any) bool {
 			cache.clear()
+			return false
 		})
 
 	return &Namespace{
diff --git a/tpl/tplimpl/embedded/templates/_hugo/build/js/batch-esm-runner.gotmpl b/tpl/tplimpl/embedded/templates/_hugo/build/js/batch-esm-runner.gotmpl
new file mode 100644
index 000000000..e1b3b9bc3
--- /dev/null
+++ b/tpl/tplimpl/embedded/templates/_hugo/build/js/batch-esm-runner.gotmpl
@@ -0,0 +1,16 @@
+{{ range $i, $e := .Scripts -}}
+  {{ printf "import { %s as Script%d } from %q;" .Export $i .Import }}
+{{ end -}}
+{{ range $i, $e := .Runners }}
+  {{ printf "import { %s as Run%d } from %q;" .Export $i .Import }}
+{{ end }}
+{{/*  */}}
+let scripts = [];
+{{ range $i, $e := .Scripts -}}
+  scripts.push({{ .RunnerJSON $i }});
+{{ end -}}
+{{/*  */}}
+{{ range $i, $e := .Runners }}
+  {{ $id := printf "Run%d" $i }}
+  {{ $id }}(scripts);
+{{ end }}
diff --git a/tpl/tplimpl/template.go b/tpl/tplimpl/template.go
index fd07db68e..9e2af046d 100644
--- a/tpl/tplimpl/template.go
+++ b/tpl/tplimpl/template.go
@@ -695,13 +695,13 @@ func (t *templateHandler) applyBaseTemplate(overlay, base templateInfo) (tpl.Tem
 		if !base.IsZero() {
 			templ, err = templ.Parse(base.template)
 			if err != nil {
-				return nil, base.errWithFileContext("parse failed", err)
+				return nil, base.errWithFileContext("text: base: parse failed", err)
 			}
 		}
 
 		templ, err = texttemplate.Must(templ.Clone()).Parse(overlay.template)
 		if err != nil {
-			return nil, overlay.errWithFileContext("parse failed", err)
+			return nil, overlay.errWithFileContext("text: overlay: parse failed", err)
 		}
 
 		// The extra lookup is a workaround, see
@@ -720,13 +720,13 @@ func (t *templateHandler) applyBaseTemplate(overlay, base templateInfo) (tpl.Tem
 	if !base.IsZero() {
 		templ, err = templ.Parse(base.template)
 		if err != nil {
-			return nil, base.errWithFileContext("parse failed", err)
+			return nil, base.errWithFileContext("html: base: parse failed", err)
 		}
 	}
 
 	templ, err = htmltemplate.Must(templ.Clone()).Parse(overlay.template)
 	if err != nil {
-		return nil, overlay.errWithFileContext("parse failed", err)
+		return nil, overlay.errWithFileContext("html: overlay: parse failed", err)
 	}
 
 	// The extra lookup is a workaround, see
diff --git a/tpl/tplimpl/template_funcs.go b/tpl/tplimpl/template_funcs.go
index 3daba74a0..d73d4d336 100644
--- a/tpl/tplimpl/template_funcs.go
+++ b/tpl/tplimpl/template_funcs.go
@@ -251,6 +251,9 @@ func newTemplateExecuter(d *deps.Deps) (texttemplate.Executer, map[string]reflec
 }
 
 func createFuncMap(d *deps.Deps) map[string]any {
+	if d.TmplFuncMap != nil {
+		return d.TmplFuncMap
+	}
 	funcMap := template.FuncMap{}
 
 	nsMap := make(map[string]any)
@@ -292,5 +295,7 @@ func createFuncMap(d *deps.Deps) map[string]any {
 		}
 	}
 
-	return funcMap
+	d.TmplFuncMap = funcMap
+
+	return d.TmplFuncMap
 }