diff --git a/src/ast.zig b/src/ast.zig
index 9cafcfa7fe..2513498aab 100644
--- a/src/ast.zig
+++ b/src/ast.zig
@@ -345,6 +345,18 @@ pub const ExportsKind = enum {
pub fn jsonStringify(self: @This(), writer: anytype) !void {
return try writer.write(@tagName(self));
}
+
+ pub fn toModuleType(self: @This()) bun.options.ModuleType {
+ return switch (self) {
+ .none => .unknown,
+ .cjs => .cjs,
+
+ .esm_with_dynamic_fallback,
+ .esm_with_dynamic_fallback_from_cjs,
+ .esm,
+ => .esm,
+ };
+ }
};
pub const DeclaredSymbol = struct {
diff --git a/src/ast/maybe.zig b/src/ast/maybe.zig
index 1c461b3099..8942a02432 100644
--- a/src/ast/maybe.zig
+++ b/src/ast/maybe.zig
@@ -411,7 +411,7 @@ pub fn AstMaybe(
}
// Inline import.meta properties for Bake
- if (p.options.framework != null) {
+ if (p.options.framework != null or (p.options.bundle and p.options.output_format == .cjs)) {
if (strings.eqlComptime(name, "dir") or strings.eqlComptime(name, "dirname")) {
// Inline import.meta.dir
return p.newExpr(E.String.init(p.source.path.name.dir), name_loc);
diff --git a/src/bundler/LinkerContext.zig b/src/bundler/LinkerContext.zig
index 59daa3f21b..8b5e8aba8f 100644
--- a/src/bundler/LinkerContext.zig
+++ b/src/bundler/LinkerContext.zig
@@ -1324,6 +1324,7 @@ pub const LinkerContext = struct {
.minify_whitespace = c.options.minify_whitespace,
.minify_syntax = c.options.minify_syntax,
+ .input_module_type = ast.exports_kind.toModuleType(),
.module_type = c.options.output_format,
.print_dce_annotations = c.options.emit_dce_annotations,
.has_run_symbol_renamer = true,
diff --git a/src/js_printer.zig b/src/js_printer.zig
index b02bf0d7f6..ebe08d3d59 100644
--- a/src/js_printer.zig
+++ b/src/js_printer.zig
@@ -414,6 +414,9 @@ pub const Options = struct {
require_or_import_meta_for_source_callback: RequireOrImportMeta.Callback = .{},
+ /// The module type of the importing file (after linking), used to determine interop helper behavior.
+ /// Controls whether __toESM uses Node ESM semantics (isNodeMode=1 for .esm) or respects __esModule markers.
+ input_module_type: options.ModuleType = .unknown,
module_type: options.Format = .esm,
// /// Used for cross-module inlining of import items when bundling
@@ -1711,7 +1714,7 @@ fn NewPrinter(
}
if (wrap_with_to_esm) {
- if (module_type.isESM()) {
+ if (p.options.input_module_type == .esm) {
p.print(",");
p.printSpace();
p.print("1");
diff --git a/test/bundler/bundler_cjs.test.ts b/test/bundler/bundler_cjs.test.ts
new file mode 100644
index 0000000000..1579d1dad4
--- /dev/null
+++ b/test/bundler/bundler_cjs.test.ts
@@ -0,0 +1,494 @@
+import { describe } from "bun:test";
+import { itBundled } from "./expectBundled";
+
+// Tests for CommonJS <> ESM interop, specifically the __toESM helper behavior.
+//
+// The key insight from the code change:
+// - `input_module_type` is set based on the AST's exports_kind (whether the importing
+// file uses ESM syntax like import/export or CJS syntax like require/module.exports)
+// - When a file uses ESM syntax (import/export), isNodeMode = 1
+// - When a file uses CJS syntax (require), __toESM is not used at all
+//
+// This means:
+// - Any file using `import` will always get isNodeMode=1, which IGNORES __esModule
+// and always wraps the CJS module as the default export
+// - This matches Node.js ESM behavior where importing CJS from .mjs always wraps
+// the entire exports object as the default
+//
+// The __esModule marker is only respected in non-bundled scenarios or when using
+// actual CommonJS require() syntax.
+
+describe("bundler", () => {
+ // ============================================================================
+ // Tests with ESM syntax (import statements)
+ // These all use isNodeMode=1, which IGNORES __esModule
+ // ============================================================================
+
+ // Test 1: import with __esModule marker - IGNORED
+ itBundled("cjs/__toESM_import_syntax_with_esModule", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.__esModule = true;
+ exports.default = { value: 'default export' };
+ exports.named = 'named export';
+ `,
+ },
+ run: {
+ // With import syntax, isNodeMode=1, so __esModule is IGNORED
+ // The entire CJS exports object is wrapped as default
+ stdout: '{"__esModule":true,"default":{"value":"default export"},"named":"named export"}',
+ },
+ });
+
+ // Test 2: import WITHOUT __esModule marker
+ itBundled("cjs/__toESM_import_syntax_without_esModule", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.foo = 'foo';
+ exports.bar = 'bar';
+ `,
+ },
+ run: {
+ // Same behavior - entire module wrapped as default
+ stdout: '{"foo":"foo","bar":"bar"}',
+ },
+ });
+
+ // Test 3: import with module.exports = function
+ itBundled("cjs/__toESM_import_syntax_function", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(lib.name + ':' + lib());
+ `,
+ "/lib.cjs": /* js */ `
+ module.exports = function myFunc() { return 'result'; };
+ `,
+ },
+ run: {
+ stdout: "myFunc:result",
+ },
+ });
+
+ // Test 4: import with module.exports = primitive
+ itBundled("cjs/__toESM_import_syntax_primitive", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(lib);
+ `,
+ "/lib.cjs": /* js */ `
+ module.exports = 42;
+ `,
+ },
+ run: {
+ stdout: "42",
+ },
+ });
+
+ // Test 5: import with named + default
+ itBundled("cjs/__toESM_import_syntax_named_and_default", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib, { foo } from './lib.cjs';
+ console.log(JSON.stringify({ default: lib, named: foo }));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.foo = 'foo value';
+ exports.bar = 'bar value';
+ `,
+ },
+ run: {
+ stdout: '{"default":{"foo":"foo value","bar":"bar value"},"named":"foo value"}',
+ },
+ });
+
+ // Test 6: Namespace import (import *)
+ itBundled("cjs/__toESM_import_syntax_namespace", {
+ files: {
+ "/entry.js": /* js */ `
+ import * as lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.foo = 'foo';
+ exports.bar = 'bar';
+ `,
+ },
+ run: {
+ // Namespace import only gets the CJS exports as-is, no default wrapper
+ stdout: '{"foo":"foo","bar":"bar"}',
+ },
+ });
+
+ // ============================================================================
+ // Tests with different targets
+ // Target doesn't affect isNodeMode - it's based on syntax
+ // ============================================================================
+
+ // Test 7: target=node
+ itBundled("cjs/__toESM_target_node", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.x = 1;
+ exports.y = 2;
+ `,
+ },
+ target: "node",
+ run: {
+ stdout: '{"x":1,"y":2}',
+ },
+ });
+
+ // Test 8: target=browser
+ itBundled("cjs/__toESM_target_browser", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.x = 1;
+ exports.y = 2;
+ `,
+ },
+ target: "browser",
+ run: {
+ stdout: '{"x":1,"y":2}',
+ },
+ });
+
+ // Test 9: target=bun
+ itBundled("cjs/__toESM_target_bun", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.x = 1;
+ exports.y = 2;
+ `,
+ },
+ target: "bun",
+ run: {
+ stdout: '{"x":1,"y":2}',
+ },
+ });
+
+ // ============================================================================
+ // Tests with different output formats
+ // Output format doesn't affect isNodeMode either
+ // ============================================================================
+
+ // Test 10: format=esm
+ itBundled("cjs/__toESM_format_esm", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.__esModule = true;
+ exports.default = 'the default';
+ exports.other = 'other';
+ `,
+ },
+ format: "esm",
+ run: {
+ // __esModule ignored because we're using import syntax
+ stdout: '{"__esModule":true,"default":"the default","other":"other"}',
+ },
+ });
+
+ // Test 11: format=cjs with import syntax
+ itBundled("cjs/__toESM_format_cjs_with_import", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.__esModule = true;
+ exports.default = 'the default';
+ exports.other = 'other';
+ `,
+ },
+ format: "cjs",
+ run: {
+ // Still ignores __esModule because entry uses import syntax
+ stdout: '{"__esModule":true,"default":"the default","other":"other"}',
+ },
+ });
+
+ // ============================================================================
+ // Tests for .mjs files re-exporting from .cjs
+ // ============================================================================
+
+ // Test 12: .mjs re-exporting default from CJS
+ itBundled("cjs/__toESM_mjs_reexport", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './wrapper.mjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/wrapper.mjs": /* js */ `
+ export { default } from './lib.cjs';
+ `,
+ "/lib.cjs": /* js */ `
+ exports.foo = 'foo';
+ exports.bar = 'bar';
+ `,
+ },
+ run: {
+ stdout: '{"foo":"foo","bar":"bar"}',
+ },
+ });
+
+ // Test 13: .mjs re-exporting with __esModule (still ignored)
+ itBundled("cjs/__toESM_mjs_reexport_with_esModule", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './wrapper.mjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/wrapper.mjs": /* js */ `
+ export { default } from './lib.cjs';
+ `,
+ "/lib.cjs": /* js */ `
+ exports.__esModule = true;
+ exports.default = { value: 'from cjs' };
+ exports.other = 'other';
+ `,
+ },
+ run: {
+ // __esModule ignored - entire module wrapped as default
+ stdout: '{"__esModule":true,"default":{"value":"from cjs"},"other":"other"}',
+ },
+ });
+
+ // Test 14: Deep re-export chain
+ itBundled("cjs/__toESM_deep_reexport_chain", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './layer1.mjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/layer1.mjs": /* js */ `
+ export { default } from './layer2.mjs';
+ `,
+ "/layer2.mjs": /* js */ `
+ export { default } from './lib.cjs';
+ `,
+ "/lib.cjs": /* js */ `
+ exports.deep = 'value';
+ `,
+ },
+ run: {
+ stdout: '{"deep":"value"}',
+ },
+ });
+
+ // Test 15: Re-export with rename
+ itBundled("cjs/__toESM_reexport_with_rename", {
+ files: {
+ "/entry.js": /* js */ `
+ import { myDefault } from './wrapper.mjs';
+ console.log(JSON.stringify(myDefault));
+ `,
+ "/wrapper.mjs": /* js */ `
+ export { default as myDefault } from './lib.cjs';
+ `,
+ "/lib.cjs": /* js */ `
+ exports.x = 1;
+ `,
+ },
+ run: {
+ stdout: '{"x":1}',
+ },
+ });
+
+ // ============================================================================
+ // Edge cases
+ // ============================================================================
+
+ // Test 16: CJS with a property named "default" but no __esModule
+ itBundled("cjs/__toESM_default_prop_no_esModule", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.default = 'I am a prop named default';
+ exports.other = 'other';
+ `,
+ },
+ run: {
+ // Entire module wrapped, including the .default property
+ stdout: '{"default":"I am a prop named default","other":"other"}',
+ },
+ });
+
+ // Test 17: Mixed import styles
+ itBundled("cjs/__toESM_mixed_import_styles", {
+ files: {
+ "/entry.js": /* js */ `
+ import defaultExport from './lib.cjs';
+ import { foo } from './lib.cjs';
+ import * as namespace from './lib.cjs';
+ console.log(JSON.stringify({
+ default: defaultExport,
+ named: foo,
+ namespace: namespace
+ }));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.foo = 'foo';
+ exports.bar = 'bar';
+ `,
+ },
+ run: {
+ stdout:
+ '{"default":{"foo":"foo","bar":"bar"},"named":"foo","namespace":{"default":{"foo":"foo","bar":"bar"},"foo":"foo","bar":"bar"}}',
+ },
+ });
+
+ // Test 18: __esModule with non-true value
+ itBundled("cjs/__toESM_esModule_non_true", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.__esModule = 'truthy';
+ exports.default = { value: 'default' };
+ exports.other = 'other';
+ `,
+ },
+ run: {
+ // Even if __esModule were respected, only `true` would work
+ // But it's ignored anyway due to import syntax
+ stdout: '{"__esModule":"truthy","default":{"value":"default"},"other":"other"}',
+ },
+ });
+
+ // Test 19: __esModule = false
+ itBundled("cjs/__toESM_esModule_false", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.__esModule = false;
+ exports.default = { value: 'ignored' };
+ exports.foo = 'foo';
+ `,
+ },
+ run: {
+ // Entire module wrapped as default (since we use import syntax)
+ stdout: '{"__esModule":false,"default":{"value":"ignored"},"foo":"foo"}',
+ },
+ });
+
+ // Test 20: module.exports with __esModule
+ itBundled("cjs/__toESM_module_exports_with_esModule", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ module.exports = {
+ __esModule: true,
+ default: { value: 'nested' },
+ other: 'prop'
+ };
+ `,
+ },
+ run: {
+ // __esModule is in the object but ignored due to import syntax
+ stdout: '{"__esModule":true,"default":{"value":"nested"},"other":"prop"}',
+ },
+ });
+
+ // Test 21: Input=ESM, output=CJS, importing CJS with __esModule and named imports
+ // This test covers the specific fix for printing __toESM when output format is CJS
+ // and input uses ESM syntax to import both default and named exports from CJS with __esModule
+ itBundled("cjs/__toESM_input_esm_output_cjs_wrapper_print", {
+ files: {
+ "/entry.js": /* js */ `
+ import lib, { named } from "./lib.cjs";
+ console.log(JSON.stringify({ default: lib, named }));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.__esModule = true;
+ exports.default = { value: "default" };
+ exports.named = "named export";
+ `,
+ },
+ format: "cjs",
+ run: {
+ // With the fix: ignores __esModule, wraps entire module as default
+ // So default gets the whole exports object, named gets the named property
+ stdout:
+ '{"default":{"__esModule":true,"default":{"value":"default"},"named":"named export"},"named":"named export"}',
+ },
+ });
+
+ // Test 22: Star import with __esModule
+ itBundled("cjs/__toESM_star_import_with_esModule", {
+ files: {
+ "/entry.js": /* js */ `
+ import * as lib from './lib.cjs';
+ console.log(JSON.stringify(lib));
+ `,
+ "/lib.cjs": /* js */ `
+ exports.__esModule = true;
+ exports.default = 'default';
+ exports.named = 'named';
+ `,
+ },
+ run: {
+ // Star import gets the exports as-is, no wrapper
+ stdout: '{"named":"named","default":"default","__esModule":true}',
+ },
+ });
+
+ // Test 23: Practical example - importing lodash-like library
+ itBundled("cjs/__toESM_practical_lodash_style", {
+ files: {
+ "/entry.js": /* js */ `
+ import _ from './lodash.cjs';
+ import { map } from './lodash.cjs';
+ console.log(JSON.stringify({
+ hasMap: typeof _.map === 'function',
+ same: _.map === map
+ }));
+ `,
+ "/lodash.cjs": /* js */ `
+ exports.map = function(arr, fn) { return arr.map(fn); };
+ exports.filter = function(arr, fn) { return arr.filter(fn); };
+ `,
+ },
+ run: {
+ // Default gets entire module, named import gets specific function
+ // Both reference the same function
+ stdout: '{"hasMap":true,"same":true}',
+ },
+ });
+});
diff --git a/test/bundler/bundler_npm.test.ts b/test/bundler/bundler_npm.test.ts
index 55fa25fb20..827081a0e8 100644
--- a/test/bundler/bundler_npm.test.ts
+++ b/test/bundler/bundler_npm.test.ts
@@ -67,7 +67,7 @@ describe("bundler", () => {
},
},
expectExactFilesize: {
- "out/entry.js": 221726,
+ "out/entry.js": 221720,
},
run: {
stdout: "Hello World
This is an example.
",