fix: cache the result of inline require() of bundled ESM modules

internal/bundler_tests/bundler_importstar_test.go

@@ -1810,6 +1810,31 @@ entry-nope.js: WARNING: Import "nope" will always be undefined because the file
 	})
 }
 
+// https://github.com/evanw/esbuild/issues/4440 — repeated `require()` of a
+// bundled ESM module must return the same wrapper object so that identity
+// matches Node.js CJS cache semantics. The inline-require path uses
+// "__toCommonJSCached" so the two `require()` calls below produce a single
+// wrapper.
+func TestRequireOfESMPreservesIdentity(t *testing.T) {
+	importstar_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				const a = require('./esm')
+				const b = require('./esm')
+				console.log(a === b)
+			`,
+			"/esm.js": `
+				export const value = 123
+			`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode:          config.ModeBundle,
+			AbsOutputFile: "/out.js",
+		},
+	})
+}
+
 // Failure case due to a bug in https://github.com/evanw/esbuild/pull/2059
 func TestReExportStarEntryPointAndInnerFile(t *testing.T) {
 	importstar_suite.expectBundled(t, bundled{

internal/bundler_tests/snapshots/snapshots_dce.txt

@@ -3002,7 +3002,7 @@ var init_cjs = __esm({
 
 // entry.js
 init_lib();
-console.log(keep1(), (init_cjs(), __toCommonJS(cjs_exports)));
+console.log(keep1(), (init_cjs(), __toCommonJSCached(cjs_exports)));
 
 ================================================================================
 TestTreeShakingJSWithAssociatedCSS

internal/bundler_tests/snapshots/snapshots_default.txt

@@ -793,9 +793,9 @@ var init_bar = __esm({
 });
 
 // entry.js
-var { foo: foo2 } = (init_foo(), __toCommonJS(foo_exports));
+var { foo: foo2 } = (init_foo(), __toCommonJSCached(foo_exports));
 console.log(foo2(), bar2());
-var { bar: bar2 } = (init_bar(), __toCommonJS(bar_exports));
+var { bar: bar2 } = (init_bar(), __toCommonJSCached(bar_exports));
 
 ================================================================================
 TestConditionalImport
@@ -1230,7 +1230,7 @@ var init_types = __esm({
 });
 
 // entry.js
-console.log((init_types(), __toCommonJS(types_exports)));
+console.log((init_types(), __toCommonJSCached(types_exports)));
 
 ================================================================================
 TestEntryNamesChunkNamesExtPlaceholder
@@ -1593,7 +1593,7 @@ var init_lib = __esm({
 });
 
 // entry.js
-var lib = (init_lib(), __toCommonJS(lib_exports));
+var lib = (init_lib(), __toCommonJSCached(lib_exports));
 console.log(lib.__proto__);
 
 ================================================================================
@@ -3858,7 +3858,7 @@ var require_cjs = __commonJS({
 // entry-cjs.js
 var require_entry_cjs = __commonJS({
   "entry-cjs.js"(exports) {
-    var { b: esm_foo_2 } = (init_esm(), __toCommonJS(esm_exports));
+    var { b: esm_foo_2 } = (init_esm(), __toCommonJSCached(esm_exports));
     var { a: cjs_foo_ } = require_cjs();
     exports.c = [
       esm_foo_2,
@@ -6561,7 +6561,7 @@ var require_es6_import_stmt = __commonJS({
 // es6-import-assign.ts
 var require_es6_import_assign = __commonJS({
   "es6-import-assign.ts"(exports) {
-    var x2 = (init_dummy(), __toCommonJS(dummy_exports));
+    var x2 = (init_dummy(), __toCommonJSCached(dummy_exports));
     console.log(exports);
   }
 });
@@ -6757,7 +6757,7 @@ console.log(void 0);
 var import_es6_export_assign = __toESM(require_es6_export_assign());
 
 // es6-export-import-assign.ts
-var x = (init_dummy(), __toCommonJS(dummy_exports));
+var x = (init_dummy(), __toCommonJSCached(dummy_exports));
 console.log(void 0);
 
 // entry.js

internal/bundler_tests/snapshots/snapshots_importstar.txt

@@ -78,7 +78,7 @@ var foo;
 var init_entry = __esm({
   "entry.js"() {
     foo = 123;
-    console.log((init_entry(), __toCommonJS(entry_exports)));
+    console.log((init_entry(), __toCommonJSCached(entry_exports)));
   }
 });
 init_entry();
@@ -459,7 +459,7 @@ var init_foo = __esm({
 
 // entry.js
 init_foo();
-var ns2 = (init_foo(), __toCommonJS(foo_exports));
+var ns2 = (init_foo(), __toCommonJSCached(foo_exports));
 console.log(foo, ns2.foo);
 
 ================================================================================
@@ -1039,3 +1039,23 @@ var x = 1;
 
 // entry.js
 console.log(x);
+
+================================================================================
+TestRequireOfESMPreservesIdentity
+---------- /out.js ----------
+// esm.js
+var esm_exports = {};
+__export(esm_exports, {
+  value: () => value
+});
+var value;
+var init_esm = __esm({
+  "esm.js"() {
+    value = 123;
+  }
+});
+
+// entry.js
+var a = (init_esm(), __toCommonJSCached(esm_exports));
+var b = (init_esm(), __toCommonJSCached(esm_exports));
+console.log(a === b);

internal/bundler_tests/snapshots/snapshots_importstar_ts.txt

@@ -14,7 +14,7 @@ var init_foo = __esm({
 
 // entry.js
 init_foo();
-var ns2 = (init_foo(), __toCommonJS(foo_exports));
+var ns2 = (init_foo(), __toCommonJSCached(foo_exports));
 console.log(foo, ns2.foo);
 
 ================================================================================

internal/bundler_tests/snapshots/snapshots_packagejson.txt

@@ -503,7 +503,7 @@ var init_module = __esm({
 });
 
 // Users/user/project/src/test-main.js
-console.log((init_module(), __toCommonJS(module_exports)));
+console.log((init_module(), __toCommonJSCached(module_exports)));
 
 // Users/user/project/src/test-module.js
 init_module();
@@ -542,7 +542,7 @@ var init_module = __esm({
 });
 
 // Users/user/project/src/test-index.js
-console.log((init_module(), __toCommonJS(module_exports)));
+console.log((init_module(), __toCommonJSCached(module_exports)));
 
 // Users/user/project/src/test-module.js
 init_module();

internal/bundler_tests/snapshots/snapshots_splitting.txt

@@ -370,26 +370,26 @@ TestSplittingHybridESMAndCJSIssue617
 import {
   foo,
   init_a
-} from "./chunk-PDZFCFBH.js";
+} from "./chunk-GBWBY5I7.js";
 init_a();
 export {
   foo
 };
 
 ---------- /out/b.js ----------
 import {
-  __toCommonJS,
+  __toCommonJSCached,
   a_exports,
   init_a
-} from "./chunk-PDZFCFBH.js";
+} from "./chunk-GBWBY5I7.js";
 
 // b.js
-var bar = (init_a(), __toCommonJS(a_exports));
+var bar = (init_a(), __toCommonJSCached(a_exports));
 export {
   bar
 };
 
----------- /out/chunk-PDZFCFBH.js ----------
+---------- /out/chunk-GBWBY5I7.js ----------
 // a.js
 var a_exports = {};
 __export(a_exports, {
@@ -402,7 +402,7 @@ var init_a = __esm({
 });
 
 export {
-  __toCommonJS,
+  __toCommonJSCached,
   foo,
   a_exports,
   init_a

internal/js_printer/js_printer.go

@@ -1583,10 +1583,13 @@ func (p *printer) printRequireOrImportExpr(importRecordIndex uint32, level js_as
 		p.print(",")
 		p.printSpace()
 
-		// Wrap this with a call to "__toCommonJS()" if this is an ESM file
+		// Wrap this with a call to "__toCommonJSCached()" if this is an ESM
+		// file. The cached variant is used (rather than "__toCommonJS") so
+		// that two require() calls for the same bundled ESM module return
+		// the same wrapper object, matching Node.js CJS cache semantics.
 		wrapWithTpCJS := record.Flags.Has(ast.WrapWithToCJS)
 		if wrapWithTpCJS {
-			p.printIdentifier(p.renamer.NameForSymbol(p.options.ToCommonJSRef))
+			p.printIdentifier(p.renamer.NameForSymbol(p.options.ToCommonJSCachedRef))
 			p.print("(")
 		}
 		p.printIdentifier(p.renamer.NameForSymbol(meta.ExportsRef))
@@ -4929,6 +4932,7 @@ type Options struct {
 	LineOffsetTables []sourcemap.LineOffsetTable
 
 	ToCommonJSRef       ast.Ref
+	ToCommonJSCachedRef ast.Ref
 	ToESMRef            ast.Ref
 	RuntimeRequireRef   ast.Ref
 	UnsupportedFeatures compat.JSFeature

internal/linker/linker.go

@@ -1979,8 +1979,11 @@ func (c *linkerContext) scanImportsAndExports() {
 			c.graph.GenerateRuntimeSymbolImportAndUse(sourceIndex, uint32(partIndex), "__toESM", toESMUses)
 
 			// If there's a CommonJS require of an ES6 module, then we're going to need the
-			// "__toCommonJS" symbol from the runtime to wrap the exports object
-			c.graph.GenerateRuntimeSymbolImportAndUse(sourceIndex, uint32(partIndex), "__toCommonJS", toCommonJSUses)
+			// "__toCommonJSCached" symbol from the runtime to wrap the exports object.
+			// The cached variant is used here (rather than "__toCommonJS") so that
+			// repeated require() of the same ESM module returns the same wrapper,
+			// matching Node.js CJS cache semantics.
+			c.graph.GenerateRuntimeSymbolImportAndUse(sourceIndex, uint32(partIndex), "__toCommonJSCached", toCommonJSUses)
 
 			// If there are unbundled calls to "require()" and we're not generating
 			// code for node, then substitute a "__require" wrapper for "require".
@@ -4659,6 +4662,7 @@ func (c *linkerContext) generateCodeForFileInChunkJS(
 	waitGroup *sync.WaitGroup,
 	partRange partRange,
 	toCommonJSRef ast.Ref,
+	toCommonJSCachedRef ast.Ref,
 	toESMRef ast.Ref,
 	runtimeRequireRef ast.Ref,
 	result *compileResultJS,
@@ -4957,6 +4961,7 @@ func (c *linkerContext) generateCodeForFileInChunkJS(
 		LineLimit:                    c.options.LineLimit,
 		ASCIIOnly:                    c.options.ASCIIOnly,
 		ToCommonJSRef:                toCommonJSRef,
+		ToCommonJSCachedRef:          toCommonJSCachedRef,
 		ToESMRef:                     toESMRef,
 		RuntimeRequireRef:            runtimeRequireRef,
 		TSEnums:                      c.graph.TSEnums,
@@ -5577,6 +5582,7 @@ func (c *linkerContext) generateChunkJS(chunkIndex int, chunkWaitGroup *sync.Wai
 	compileResults := make([]compileResultJS, 0, len(chunkRepr.partsInChunkInOrder))
 	runtimeMembers := c.graph.Files[runtime.SourceIndex].InputFile.Repr.(*graph.JSRepr).AST.ModuleScope.Members
 	toCommonJSRef := ast.FollowSymbols(c.graph.Symbols, runtimeMembers["__toCommonJS"].Ref)
+	toCommonJSCachedRef := ast.FollowSymbols(c.graph.Symbols, runtimeMembers["__toCommonJSCached"].Ref)
 	toESMRef := ast.FollowSymbols(c.graph.Symbols, runtimeMembers["__toESM"].Ref)
 	runtimeRequireRef := ast.FollowSymbols(c.graph.Symbols, runtimeMembers["__require"].Ref)
 	r := c.renameSymbolsInChunk(chunk, chunkRepr.filesInChunkInOrder, timer)
@@ -5609,6 +5615,7 @@ func (c *linkerContext) generateChunkJS(chunkIndex int, chunkWaitGroup *sync.Wai
 			&waitGroup,
 			partRange,
 			toCommonJSRef,
+			toCommonJSCachedRef,
 			toESMRef,
 			runtimeRequireRef,
 			compileResult,

internal/runtime/runtime.go

@@ -246,6 +246,17 @@ func Source(unsupportedJSFeatures compat.JSFeature) logger.Source {
 		// to "true", which overwrites any existing export named "__esModule".
 		export var __toCommonJS = mod => __copyProps(__defProp({}, '__esModule', { value: true }), mod)
 
+		// Same conversion as __toCommonJS but memoized. Used for inline
+		// "require()" of a bundled ESM module, where the call is emitted at
+		// every require site; without the cache, two require() calls for the
+		// same module would return distinct objects, breaking Node.js CJS
+		// cache semantics. Falls back to no cache when WeakMap is unavailable.
+		export var __toCommonJSCached = /* @__PURE__ */ (cache => (mod, result) => (
+			cache && (result = cache.get(mod)) || (
+				result = __toCommonJS(mod), cache && cache.set(mod, result)),
+			result
+		))(typeof WeakMap !== 'undefined' ? new WeakMap : 0)
+
 		// For TypeScript experimental decorators
 		// - kind === undefined: class
 		// - kind === 1: method, parameter