esm: add --import flag

PR-URL: #43942
Fixes: #40110
Reviewed-By: Geoffrey Booth <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Jacob Smith <[email protected]>
Reviewed-By: Antoine du Hamel <[email protected]>

Author: MoLow

doc/api/cli.md

@@ -445,7 +445,8 @@ Only the root context is supported. There is no guarantee that
 `globalThis.Array` is indeed the default intrinsic reference. Code may break
 under this flag.
 
-To allow polyfills to be added, `--require` runs before freezing intrinsics.
+To allow polyfills to be added,
+[`--require`][] and [`--import`][] both run before freezing intrinsics.
 
 ### `--force-node-api-uncaught-exceptions-policy`
 
@@ -594,6 +595,18 @@ added: v0.11.15
 
 Specify ICU data load path. (Overrides `NODE_ICU_DATA`.)
 
+### `--import=module`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Preload the specified module at startup.
+
+Follows [ECMAScript module][] resolution rules.
+Use [`--require`][] to load a [CommonJS module][].
+Modules preloaded with `--require` will run before modules preloaded with `--import`.
+
 ### `--input-type=type`
 
 <!-- YAML
@@ -1527,8 +1540,9 @@ Preload the specified module at startup.
 Follows `require()`'s module resolution
 rules. `module` may be either a path to a file, or a node module name.
 
-Only CommonJS modules are supported. Attempting to preload a
-ES6 Module using `--require` will fail with an error.
+Only CommonJS modules are supported.
+Use [`--import`][] to preload an [ECMAScript module][].
+Modules preloaded with `--require` will run before modules preloaded with `--import`.
 
 ### `-v`, `--version`
 
@@ -1682,6 +1696,7 @@ Node.js options that are allowed are:
 * `--heapsnapshot-signal`
 * `--http-parser`
 * `--icu-data-dir`
+* `--import`
 * `--input-type`
 * `--insecure-http-parser`
 * `--inspect-brk`
@@ -2086,7 +2101,9 @@ done
 [#42511]: https://github.com/nodejs/node/issues/42511
 [Chrome DevTools Protocol]: https://chromedevtools.github.io/devtools-protocol/
 [CommonJS]: modules.md
+[CommonJS module]: modules.md
 [CustomEvent Web API]: https://dom.spec.whatwg.org/#customevent
+[ECMAScript module]: esm.md#modules-ecmascript-modules
 [ECMAScript module loader]: esm.md#loaders
 [Fetch API]: https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API
 [Modules loaders]: packages.md#modules-loaders
@@ -2103,8 +2120,10 @@ done
 [`--diagnostic-dir`]: #--diagnostic-dirdirectory
 [`--experimental-wasm-modules`]: #--experimental-wasm-modules
 [`--heap-prof-dir`]: #--heap-prof-dir
+[`--import`]: #--importmodule
 [`--openssl-config`]: #--openssl-configfile
 [`--redirect-warnings`]: #--redirect-warningsfile
+[`--require`]: #-r---require-module
 [`Atomics.wait()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Atomics/wait
 [`Buffer`]: buffer.md#class-buffer
 [`CRYPTO_secure_malloc_init`]: https://www.openssl.org/docs/man1.1.0/man3/CRYPTO_secure_malloc_init.html

lib/internal/main/check_syntax.js

@@ -3,6 +3,7 @@
 // If user passed `-c` or `--check` arguments to Node, check its syntax
 // instead of actually running the file.
 
+const { getOptionValue } = require('internal/options');
 const {
   prepareMainThreadExecution
 } = require('internal/bootstrap/pre_execution');
@@ -36,18 +37,29 @@ if (process.argv[1] && process.argv[1] !== '-') {
 
   markBootstrapComplete();
 
-  checkSyntax(source, filename);
+  loadESMIfNeeded(() => checkSyntax(source, filename));
 } else {
   markBootstrapComplete();
 
-  readStdin((code) => {
+  loadESMIfNeeded(() => readStdin((code) => {
     checkSyntax(code, '[stdin]');
-  });
+  }));
 }
 
-async function checkSyntax(source, filename) {
+function loadESMIfNeeded(cb) {
   const { getOptionValue } = require('internal/options');
-  let isModule = false;
+  const hasModulePreImport = getOptionValue('--import').length > 0;
+
+  if (hasModulePreImport) {
+    const { loadESM } = require('internal/process/esm_loader');
+    loadESM(cb);
+    return;
+  }
+  cb();
+}
+
+async function checkSyntax(source, filename) {
+  let isModule = true;
   if (filename === '[stdin]' || filename === '[eval]') {
     isModule = getOptionValue('--input-type') === 'module';
   } else {
@@ -57,11 +69,14 @@ async function checkSyntax(source, filename) {
     const format = await defaultGetFormat(url);
     isModule = format === 'module';
   }
+
   if (isModule) {
     const { ModuleWrap } = internalBinding('module_wrap');
     new ModuleWrap(filename, undefined, source, 0, 0);
     return;
   }
 
-  wrapSafe(filename, source);
+  const { loadESM } = require('internal/process/esm_loader');
+  const { handleMainPromise } = require('internal/modules/run_main');
+  handleMainPromise(loadESM((loader) => wrapSafe(filename, source)));
 }

lib/internal/main/eval_stdin.js

@@ -23,11 +23,13 @@ readStdin((code) => {
   process._eval = code;
 
   const print = getOptionValue('--print');
+  const loadESM = getOptionValue('--import').length > 0;
   if (getOptionValue('--input-type') === 'module')
     evalModule(code, print);
   else
     evalScript('[stdin]',
                code,
                getOptionValue('--inspect-brk'),
-               print);
+               print,
+               loadESM);
 });

lib/internal/main/eval_string.js

@@ -21,10 +21,12 @@ markBootstrapComplete();
 
 const source = getOptionValue('--eval');
 const print = getOptionValue('--print');
+const loadESM = getOptionValue('--import').length > 0;
 if (getOptionValue('--input-type') === 'module')
   evalModule(source, print);
 else
   evalScript('[eval]',
              source,
              getOptionValue('--inspect-brk'),
-             print);
+             print,
+             loadESM);

lib/internal/modules/run_main.js

@@ -33,7 +33,12 @@ function shouldUseESMLoader(mainPath) {
    * (or an empty list when none have been registered).
    */
   const userLoaders = getOptionValue('--experimental-loader');
-  if (userLoaders.length > 0)
+  /**
+   * @type {string[]} userImports A list of preloaded modules registered by the user
+   * (or an empty list when none have been registered).
+   */
+  const userImports = getOptionValue('--import');
+  if (userLoaders.length > 0 || userImports.length > 0)
     return true;
   const esModuleSpecifierResolution =
     getOptionValue('--experimental-specifier-resolution');

lib/internal/process/esm_loader.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const {
+  ArrayIsArray,
   ObjectCreate,
 } = primordials;
 
@@ -56,8 +57,23 @@ async function initializeLoader() {
 
   const { getOptionValue } = require('internal/options');
   const customLoaders = getOptionValue('--experimental-loader');
+  const preloadModules = getOptionValue('--import');
+  const loaders = await loadModulesInIsolation(customLoaders);
 
-  if (customLoaders.length === 0) return;
+  // Hooks must then be added to external/public loader
+  // (so they're triggered in userland)
+  esmLoader.addCustomLoaders(loaders);
+
+  // Preload after loaders are added so they can be used
+  if (preloadModules?.length) {
+    await loadModulesInIsolation(preloadModules, loaders);
+  }
+
+  isESMInitialized = true;
+}
+
+function loadModulesInIsolation(specifiers, loaders = []) {
+  if (!ArrayIsArray(specifiers) || specifiers.length === 0) { return; }
 
   let cwd;
   try {
@@ -70,19 +86,14 @@ async function initializeLoader() {
   // between internal Node.js and userland. For example, a module with internal
   // state (such as a counter) should be independent.
   const internalEsmLoader = new ESMLoader();
+  internalEsmLoader.addCustomLoaders(loaders);
 
   // Importation must be handled by internal loader to avoid poluting userland
-  const keyedExportsList = await internalEsmLoader.import(
-    customLoaders,
+  return internalEsmLoader.import(
+    specifiers,
     pathToFileURL(cwd).href,
     ObjectCreate(null),
   );
-
-  // Hooks must then be added to external/public loader
-  // (so they're triggered in userland)
-  await esmLoader.addCustomLoaders(keyedExportsList);
-
-  isESMInitialized = true;
 }
 
 exports.loadESM = async function loadESM(callback) {

lib/internal/process/execution.js

@@ -48,7 +48,7 @@ function evalModule(source, print) {
   return handleMainPromise(loadESM((loader) => loader.eval(source)));
 }
 
-function evalScript(name, body, breakFirstLine, print) {
+function evalScript(name, body, breakFirstLine, print, shouldLoadESM = false) {
   const CJSModule = require('internal/modules/cjs/loader').Module;
   const { kVmBreakFirstLineSymbol } = require('internal/util');
   const { pathToFileURL } = require('url');
@@ -60,35 +60,44 @@ function evalScript(name, body, breakFirstLine, print) {
   module.filename = path.join(cwd, name);
   module.paths = CJSModule._nodeModulePaths(cwd);
 
+  const { handleMainPromise } = require('internal/modules/run_main');
   const asyncESM = require('internal/process/esm_loader');
   const baseUrl = pathToFileURL(module.filename).href;
+  const { loadESM } = asyncESM;
+
+  const runScript = () => {
+    // Create wrapper for cache entry
+    const script = `
+      globalThis.module = module;
+      globalThis.exports = exports;
+      globalThis.__dirname = __dirname;
+      globalThis.require = require;
+      return (main) => main();
+    `;
+    globalThis.__filename = name;
+    const result = module._compile(script, `${name}-wrapper`)(() =>
+      require('vm').runInThisContext(body, {
+        filename: name,
+        displayErrors: true,
+        [kVmBreakFirstLineSymbol]: !!breakFirstLine,
+        importModuleDynamically(specifier, _, importAssertions) {
+          const loader = asyncESM.esmLoader;
+          return loader.import(specifier, baseUrl, importAssertions);
+        }
+      }));
+    if (print) {
+      const { log } = require('internal/console/global');
+      log(result);
+    }
 
-  // Create wrapper for cache entry
-  const script = `
-    globalThis.module = module;
-    globalThis.exports = exports;
-    globalThis.__dirname = __dirname;
-    globalThis.require = require;
-    return (main) => main();
-  `;
-  globalThis.__filename = name;
-  const result = module._compile(script, `${name}-wrapper`)(() =>
-    require('vm').runInThisContext(body, {
-      filename: name,
-      displayErrors: true,
-      [kVmBreakFirstLineSymbol]: !!breakFirstLine,
-      importModuleDynamically(specifier, _, importAssertions) {
-        const loader = asyncESM.esmLoader;
-        return loader.import(specifier, baseUrl, importAssertions);
-      }
-    }));
-  if (print) {
-    const { log } = require('internal/console/global');
-    log(result);
-  }
+    if (origModule !== undefined)
+      globalThis.module = origModule;
+  };
 
-  if (origModule !== undefined)
-    globalThis.module = origModule;
+  if (shouldLoadESM) {
+    return handleMainPromise(loadESM(runScript));
+  }
+  return runScript();
 }
 
 const exceptionHandlerState = {

src/node_options.cc

@@ -608,10 +608,14 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
   AddAlias("-pe", { "--print", "--eval" });
   AddAlias("-p", "--print");
   AddOption("--require",
-            "module to preload (option can be repeated)",
-            &EnvironmentOptions::preload_modules,
+            "CommonJS module to preload (option can be repeated)",
+            &EnvironmentOptions::preload_cjs_modules,
             kAllowedInEnvironment);
   AddAlias("-r", "--require");
+  AddOption("--import",
+            "ES module to preload (option can be repeated)",
+            &EnvironmentOptions::preload_esm_modules,
+            kAllowedInEnvironment);
   AddOption("--interactive",
             "always enter the REPL even if stdin does not appear "
             "to be a terminal",

src/node_options.h

@@ -188,7 +188,9 @@ class EnvironmentOptions : public Options {
   bool tls_max_v1_3 = false;
   std::string tls_keylog;
 
-  std::vector<std::string> preload_modules;
+  std::vector<std::string> preload_cjs_modules;
+
+  std::vector<std::string> preload_esm_modules;
 
   std::vector<std::string> user_argv;