Prefix Node.js built-in imports with node: (emscripten-core#26079)

To ensure compatibility with Deno which requires explicit
identification of built-in Node.js modules.

When targeting Node.js versions older than 16 (e.g.
`-sMIN_NODE_VERSION=150000`), the `node:` prefix is removed using
a custom Babel plugin.

Author: kleisauke

.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();
 }