Prefix Node.js built-in imports with node:

.circleci/config.yml

@@ -890,6 +890,8 @@ jobs:
             core0.test_hello_world
             core0.test_hello_argc_pthreads
             core2.test_pthread_create
+            other.test_esm
+            other.test_esm_pthreads
             "
   test-deno:
     executor: linux-python
@@ -908,6 +910,8 @@ jobs:
             core0.test_hello_world
             core0.test_hello_argc_pthreads
             core2.test_pthread_create
+            other.test_esm
+            other.test_esm_pthreads
             "
   test-jsc:
     executor: linux-python

src/babel-plugins/strip-node-prefix.mjs

@@ -0,0 +1,48 @@
+/**
+ * @license
+ * Copyright 2026 The Emscripten Authors
+ * SPDX-License-Identifier: MIT
+ */
+
+// A babel plugin to remove the leading `node:` prefix from all imports.
+
+export default function ({ types: t, targets }) {
+  // Skip this plugin for Node.js >= 16
+  if (+targets().node.split('.')[0] >= 16) {
+    return {};
+  }
+
+  return {
+    name: 'strip-node-prefix',
+    visitor: {
+      // e.g. `import fs from 'node:fs'`
+      ImportDeclaration({ node }) {
+        if (node.source.value.startsWith('node:')) {
+          node.source.value = node.source.value.slice(5);
+        }
+      },
+
+      // e.g. `await import('node:fs')`
+      // Note: only here for reference, it's mangled with EMSCRIPTEN$AWAIT$IMPORT below.
+      ImportExpression({ node }) {
+        if (t.isStringLiteral(node.source) && node.source.value.startsWith('node:')) {
+          node.source.value = node.source.value.slice(5);
+        }
+      },
+
+      // e.g. `require('node:fs')` or EMSCRIPTEN$AWAIT$IMPORT('node:fs')
+      CallExpression({ node }) {
+        if (
+          (t.isIdentifier(node.callee, { name: 'require' }) ||
+            // Special placeholder for `await import`
+            // FIXME: Remove after PR https://github.com/emscripten-core/emscripten/pull/23730 is landed.
+            t.isIdentifier(node.callee, { name: 'EMSCRIPTEN$AWAIT$IMPORT' })) &&
+          t.isStringLiteral(node.arguments[0]) &&
+          node.arguments[0].value.startsWith('node:')
+        ) {
+          node.arguments[0].value = node.arguments[0].value.slice(5);
+        }
+      },
+    },
+  };
+}

src/lib/libatomic.js

@@ -161,7 +161,7 @@ addToLibrary({
 
   emscripten_num_logical_cores: () =>
 #if ENVIRONMENT_MAY_BE_NODE
-    ENVIRONMENT_IS_NODE ? require('os').cpus().length :
+    ENVIRONMENT_IS_NODE ? require('node:os').cpus().length :
 #endif
     navigator['hardwareConcurrency'],
 });

src/lib/libcore.js

@@ -351,7 +351,7 @@ addToLibrary({
       var cmdstr = UTF8ToString(command);
       if (!cmdstr.length) return 0; // this is what glibc seems to do (shell works test?)
 
-      var cp = require('child_process');
+      var cp = require('node:child_process');
       var ret = cp.spawnSync(cmdstr, [], {shell:true, stdio:'inherit'});
 
       var _W_EXITCODE = (ret, sig) => ((ret) << 8 | (sig));

src/lib/libembind_gen.js

@@ -922,7 +922,7 @@ var LibraryEmbind = {
     const printer = new TsPrinter(moduleDefinitions);
 #endif
     const output = printer.print();
-    var fs = require('fs');
+    var fs = require('node:fs');
     fs.writeFileSync(process.argv[2], output + '\n');
   },
 

src/lib/libnodepath.js

@@ -12,7 +12,7 @@
 // operations. Hence, using `nodePath` should be safe here.
 
 addToLibrary({
-  $nodePath: "require('path')",
+  $nodePath: "require('node:path')",
   $PATH__deps: ['$nodePath'],
   $PATH: `{
     isAbs: nodePath.isAbsolute,

src/lib/libwasi.js

@@ -571,7 +571,7 @@ var WasiLibrary = {
 #if ENVIRONMENT_MAY_BE_NODE && MIN_NODE_VERSION < 190000
     // This block is not needed on v19+ since crypto.getRandomValues is builtin
     if (ENVIRONMENT_IS_NODE) {
-      var nodeCrypto = require('crypto');
+      var nodeCrypto = require('node:crypto');
       return (view) => nodeCrypto.randomFillSync(view);
     }
 #endif // ENVIRONMENT_MAY_BE_NODE

src/lib/libwasm_worker.js

@@ -286,7 +286,7 @@ if (ENVIRONMENT_IS_WASM_WORKER
 
   emscripten_navigator_hardware_concurrency: () => {
 #if ENVIRONMENT_MAY_BE_NODE
-    if (ENVIRONMENT_IS_NODE) return require('os').cpus().length;
+    if (ENVIRONMENT_IS_NODE) return require('node:os').cpus().length;
 #endif
     return navigator['hardwareConcurrency'];
   },

src/parseTools.mjs

@@ -1140,19 +1140,19 @@ function nodePthreadDetection() {
   // Under node we detect that we are running in a pthread by checking the
   // workerData property.
   if (EXPORT_ES6) {
-    return "(await import('worker_threads')).workerData === 'em-pthread'";
+    return "(await import('node:worker_threads')).workerData === 'em-pthread'";
   } else {
-    return "require('worker_threads').workerData === 'em-pthread'";
+    return "require('node:worker_threads').workerData === 'em-pthread'";
   }
 }
 
 function nodeWWDetection() {
   // Under node we detect that we are running in a wasm worker by checking the
   // workerData property.
   if (EXPORT_ES6) {
-    return "(await import('worker_threads')).workerData === 'em-ww'";
+    return "(await import('node:worker_threads')).workerData === 'em-ww'";
   } else {
-    return "require('worker_threads').workerData === 'em-ww'";
+    return "require('node:worker_threads').workerData === 'em-ww'";
   }
 }
 

src/postamble.js

@@ -322,7 +322,7 @@ if (ENVIRONMENT_IS_NODE
 #endif
 )
 {
-  const url = await import('url');
+  const url = await import('node:url');
   const isMainModule = url.pathToFileURL(process.argv[1]).href === import.meta.url;
   if (isMainModule) await init();
 }

src/preamble.js

@@ -555,7 +555,7 @@ function instantiateSync(file, info) {
   var binary = getBinarySync(file);
 #if NODE_CODE_CACHING
   if (ENVIRONMENT_IS_NODE) {
-    var v8 = require('v8');
+    var v8 = require('node:v8');
     // Include the V8 version in the cache name, so that we don't try to
     // load cached code from another version, which fails silently (it seems
     // to load ok, but we do actually recompile the binary every time).

src/pthread_esm_startup.mjs

@@ -17,7 +17,7 @@ console.log("Running pthread_esm_startup");
 if ({{{ nodeDetectionCode() }}}) {
   // Create as web-worker-like an environment as we can.
   globalThis.self = globalThis;
-  var worker_threads = await import('worker_threads');
+  var worker_threads = await import('node:worker_threads');
   globalThis.Worker = worker_threads.Worker;
   var parentPort = worker_threads['parentPort'];
   // Deno and Bun already have `postMessage` defined on the global scope and

src/runtime_debug.js

@@ -15,8 +15,8 @@ function dbg(...args) {
   // See https://github.com/emscripten-core/emscripten/issues/14804
   if (ENVIRONMENT_IS_NODE) {
     // TODO(sbc): Unify with err/out implementation in shell.sh.
-    var fs = require('fs');
-    var utils = require('util');
+    var fs = require('node:fs');
+    var utils = require('node:util');
     function stringify(a) {
       switch (typeof a) {
         case 'object': return utils.inspect(a);

src/shell.js

@@ -112,13 +112,13 @@ if (ENVIRONMENT_IS_NODE) {
 #if EXPORT_ES6
   // When building an ES module `require` is not normally available.
   // We need to use `createRequire()` to construct the require()` function.
-  const { createRequire } = await import('module');
+  const { createRequire } = await import('node:module');
   /** @suppress{duplicate} */
   var require = createRequire(import.meta.url);
 #endif
 
 #if PTHREADS || WASM_WORKERS
-  var worker_threads = require('worker_threads');
+  var worker_threads = require('node:worker_threads');
   global.Worker = worker_threads.Worker;
   ENVIRONMENT_IS_WORKER = !worker_threads.isMainThread;
 #if PTHREADS
@@ -200,11 +200,11 @@ if (ENVIRONMENT_IS_NODE) {
 
   // These modules will usually be used on Node.js. Load them eagerly to avoid
   // the complexity of lazy-loading.
-  var fs = require('fs');
+  var fs = require('node:fs');
 
 #if EXPORT_ES6
   if (_scriptName.startsWith('file:')) {
-    scriptDirectory = require('path').dirname(require('url').fileURLToPath(_scriptName)) + '/';
+    scriptDirectory = require('node:path').dirname(require('node:url').fileURLToPath(_scriptName)) + '/';
   }
 #else
   scriptDirectory = __dirname + '/';
@@ -376,7 +376,7 @@ if (!ENVIRONMENT_IS_AUDIO_WORKLET)
 var defaultPrint = console.log.bind(console);
 var defaultPrintErr = console.error.bind(console);
 if (ENVIRONMENT_IS_NODE) {
-  var utils = require('util');
+  var utils = require('node:util');
   var stringify = (a) => typeof a == 'object' ? utils.inspect(a) : a;
   defaultPrint = (...args) => fs.writeSync(1, args.map(stringify).join(' ') + '\n');
   defaultPrintErr = (...args) => fs.writeSync(2, args.map(stringify).join(' ') + '\n');

src/shell_minimal.js

@@ -55,7 +55,7 @@ var ENVIRONMENT_IS_WEB = !ENVIRONMENT_IS_NODE;
 
 #if ENVIRONMENT_MAY_BE_NODE && (PTHREADS || WASM_WORKERS)
 if (ENVIRONMENT_IS_NODE) {
-  var worker_threads = require('worker_threads');
+  var worker_threads = require('node:worker_threads');
   global.Worker = worker_threads.Worker;
 }
 #endif
@@ -99,7 +99,7 @@ if (ENVIRONMENT_IS_NODE && ENVIRONMENT_IS_SHELL) {
 var defaultPrint = console.log.bind(console);
 var defaultPrintErr = console.error.bind(console);
 if (ENVIRONMENT_IS_NODE) {
-  var fs = require('fs');
+  var fs = require('node:fs');
   defaultPrint = (...args) => fs.writeSync(1, args.join(' ') + '\n');
   defaultPrintErr = (...args) => fs.writeSync(2, args.join(' ') + '\n');
 }
@@ -181,7 +181,7 @@ if (!ENVIRONMENT_IS_PTHREAD) {
 // Wasm or Wasm2JS loading:
 
 if (ENVIRONMENT_IS_NODE) {
-  var fs = require('fs');
+  var fs = require('node:fs');
 #if WASM == 2
   if (globalThis.WebAssembly) Module['wasm'] = fs.readFileSync(__dirname + '/{{{ TARGET_BASENAME }}}.wasm');
   else eval(fs.readFileSync(__dirname + '/{{{ TARGET_BASENAME }}}.wasm.js')+'');

test/codesize/test_codesize_cxx_ctors1.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 19654,
-  "a.out.js.gz": 8145,
+  "a.out.js": 19664,
+  "a.out.js.gz": 8146,
   "a.out.nodebug.wasm": 133734,
   "a.out.nodebug.wasm.gz": 51516,
-  "total": 153388,
-  "total_gz": 59661,
+  "total": 153398,
+  "total_gz": 59662,
   "sent": [
     "__cxa_throw",
     "_abort_js",

test/codesize/test_codesize_cxx_ctors2.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 19631,
-  "a.out.js.gz": 8132,
+  "a.out.js": 19641,
+  "a.out.js.gz": 8133,
   "a.out.nodebug.wasm": 133152,
   "a.out.nodebug.wasm.gz": 51189,
-  "total": 152783,
-  "total_gz": 59321,
+  "total": 152793,
+  "total_gz": 59322,
   "sent": [
     "__cxa_throw",
     "_abort_js",

test/codesize/test_codesize_cxx_except.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 23315,
-  "a.out.js.gz": 9125,
+  "a.out.js": 23325,
+  "a.out.js.gz": 9127,
   "a.out.nodebug.wasm": 175691,
   "a.out.nodebug.wasm.gz": 59682,
-  "total": 199006,
-  "total_gz": 68807,
+  "total": 199016,
+  "total_gz": 68809,
   "sent": [
     "__cxa_begin_catch",
     "__cxa_end_catch",

test/codesize/test_codesize_cxx_except_wasm.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 19470,
-  "a.out.js.gz": 8070,
+  "a.out.js": 19475,
+  "a.out.js.gz": 8072,
   "a.out.nodebug.wasm": 149098,
   "a.out.nodebug.wasm.gz": 56901,
-  "total": 168568,
-  "total_gz": 64971,
+  "total": 168573,
+  "total_gz": 64973,
   "sent": [
     "_abort_js",
     "_tzset_js",

test/codesize/test_codesize_cxx_except_wasm_legacy.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 19539,
-  "a.out.js.gz": 8089,
+  "a.out.js": 19549,
+  "a.out.js.gz": 8091,
   "a.out.nodebug.wasm": 146681,
   "a.out.nodebug.wasm.gz": 56474,
-  "total": 166220,
-  "total_gz": 64563,
+  "total": 166230,
+  "total_gz": 64565,
   "sent": [
     "_abort_js",
     "_tzset_js",

test/codesize/test_codesize_cxx_lto.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 19001,
-  "a.out.js.gz": 7824,
+  "a.out.js": 19011,
+  "a.out.js.gz": 7826,
   "a.out.nodebug.wasm": 101673,
   "a.out.nodebug.wasm.gz": 40413,
-  "total": 120674,
-  "total_gz": 48237,
+  "total": 120684,
+  "total_gz": 48239,
   "sent": [
     "a (emscripten_resize_heap)",
     "b (_setitimer_js)",

test/codesize/test_codesize_cxx_mangle.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 23365,
-  "a.out.js.gz": 9145,
+  "a.out.js": 23375,
+  "a.out.js.gz": 9147,
   "a.out.nodebug.wasm": 239944,
   "a.out.nodebug.wasm.gz": 81208,
-  "total": 263309,
-  "total_gz": 90353,
+  "total": 263319,
+  "total_gz": 90355,
   "sent": [
     "__cxa_begin_catch",
     "__cxa_end_catch",

test/codesize/test_codesize_cxx_noexcept.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 19654,
-  "a.out.js.gz": 8145,
+  "a.out.js": 19664,
+  "a.out.js.gz": 8146,
   "a.out.nodebug.wasm": 136307,
   "a.out.nodebug.wasm.gz": 52390,
-  "total": 155961,
-  "total_gz": 60535,
+  "total": 155971,
+  "total_gz": 60536,
   "sent": [
     "__cxa_throw",
     "_abort_js",

test/codesize/test_codesize_cxx_wasmfs.json

@@ -1,10 +1,10 @@
 {
-  "a.out.js": 7043,
-  "a.out.js.gz": 3322,
+  "a.out.js": 7053,
+  "a.out.js.gz": 3325,
   "a.out.nodebug.wasm": 174601,
   "a.out.nodebug.wasm.gz": 65335,
-  "total": 181644,
-  "total_gz": 68657,
+  "total": 181654,
+  "total_gz": 68660,
   "sent": [
     "__cxa_throw",
     "_abort_js",