lib: refactor NativeModule

Refactor the internal NativeModule class to a JS class and add
more documentation about its properties.

PR-URL: https://github.com/nodejs/node/pull/30856
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/internal/bootstrap/loaders.js

@@ -137,89 +137,83 @@ let internalBinding;
   };
 }
 
-// Think of this as module.exports in this file even though it is not
-// written in CommonJS style.
-const loaderExports = {
-  internalBinding,
-  NativeModule,
-  require: nativeModuleRequire
+const loaderId = 'internal/bootstrap/loaders';
+const {
+  moduleIds,
+  compileFunction
+} = internalBinding('native_module');
+
+const getOwn = (target, property, receiver) => {
+  return ObjectPrototypeHasOwnProperty(target, property) ?
+    ReflectGet(target, property, receiver) :
+    undefined;
 };
 
-const loaderId = 'internal/bootstrap/loaders';
+/**
+ * An internal abstraction for the built-in JavaScript modules of Node.js.
+ * Be careful not to expose this to user land unless --expose-internals is
+ * used, in which case there is no compatibility guarantee about this class.
+ */
+class NativeModule {
+  /**
+   * A map from the module IDs to the module instances.
+   * @type {Map<string, NativeModule>}
+  */
+  static map = new Map(moduleIds.map((id) => [id, new NativeModule(id)]));
 
-// Set up NativeModule.
-function NativeModule(id) {
+  constructor(id) {
     this.filename = `${id}.js`;
     this.id = id;
+    this.canBeRequiredByUsers = !id.startsWith('internal/');
+
+    // The CJS exports object of the module.
     this.exports = {};
-  this.module = undefined;
-  this.exportKeys = undefined;
+    // States used to work around circular dependencies.
     this.loaded = false;
     this.loading = false;
-  this.canBeRequiredByUsers = !id.startsWith('internal/');
-}
 
-// To be called during pre-execution when --expose-internals is on.
-// Enables the user-land module loader to access internal modules.
-NativeModule.exposeInternals = function() {
+    // The following properties are used by the ESM implementation and only
+    // initialized when the native module is loaded by users.
+    /**
+     * The C++ ModuleWrap binding used to interface with the ESM implementation.
+     * @type {ModuleWrap|undefined}
+     */
+    this.module = undefined;
+    /**
+     * Exported names for the ESM imports.
+     * @type {string[]|undefined}
+     */
+    this.exportKeys = undefined;
+  }
+
+  // To be called during pre-execution when --expose-internals is on.
+  // Enables the user-land module loader to access internal modules.
+  static exposeInternals() {
     for (const [id, mod] of NativeModule.map) {
       // Do not expose this to user land even with --expose-internals.
       if (id !== loaderId) {
         mod.canBeRequiredByUsers = true;
       }
     }
-};
-
-const {
-  moduleIds,
-  compileFunction
-} = internalBinding('native_module');
-
-NativeModule.map = new Map();
-for (let i = 0; i < moduleIds.length; ++i) {
-  const id = moduleIds[i];
-  const mod = new NativeModule(id);
-  NativeModule.map.set(id, mod);
-}
-
-function nativeModuleRequire(id) {
-  if (id === loaderId) {
-    return loaderExports;
   }
 
-  const mod = NativeModule.map.get(id);
-  // Can't load the internal errors module from here, have to use a raw error.
-  // eslint-disable-next-line no-restricted-syntax
-  if (!mod) throw new TypeError(`Missing internal module '${id}'`);
-  return mod.compile();
-}
-
-NativeModule.exists = function(id) {
+  static exists(id) {
     return NativeModule.map.has(id);
-};
+  }
 
-NativeModule.canBeRequiredByUsers = function(id) {
+  static canBeRequiredByUsers(id) {
     const mod = NativeModule.map.get(id);
     return mod && mod.canBeRequiredByUsers;
-};
-
-// Allow internal modules from dependencies to require
-// other modules from dependencies by providing fallbacks.
-function requireWithFallbackInDeps(request) {
-  if (!NativeModule.map.has(request)) {
-    request = `internal/deps/${request}`;
   }
-  return nativeModuleRequire(request);
-}
 
-// This is exposed for public loaders
-NativeModule.prototype.compileForPublicLoader = function() {
+  // Used by user-land module loaders to compile and load builtins.
+  compileForPublicLoader() {
     if (!this.canBeRequiredByUsers) {
       // No code because this is an assertion against bugs
       // eslint-disable-next-line no-restricted-syntax
       throw new Error(`Should not compile ${this.id} for public use`);
     }
-  this.compile();
+    this.compileForInternalLoader();
     if (!this.exportKeys) {
       // When using --expose-internals, we do not want to reflect the named
       // exports from core modules as this can trigger unnecessary getters.
@@ -229,22 +223,12 @@ NativeModule.prototype.compileForPublicLoader = function() {
     this.getESMFacade();
     this.syncExports();
     return this.exports;
-};
+  }
 
-const getOwn = (target, property, receiver) => {
-  return ObjectPrototypeHasOwnProperty(target, property) ?
-    ReflectGet(target, property, receiver) :
-    undefined;
-};
-
-NativeModule.prototype.getURL = function() {
-  return `node:${this.id}`;
-};
-
-NativeModule.prototype.getESMFacade = function() {
+  getESMFacade() {
     if (this.module) return this.module;
     const { ModuleWrap } = internalBinding('module_wrap');
-  const url = this.getURL();
+    const url = `node:${this.id}`;
     const nativeModule = this;
     this.module = new ModuleWrap(
       url, undefined, [...this.exportKeys, 'default'],
@@ -256,13 +240,13 @@ NativeModule.prototype.getESMFacade = function() {
     this.module.instantiate();
     this.module.evaluate(-1, false);
     return this.module;
-};
+  }
 
-// Provide named exports for all builtin libraries so that the libraries
-// may be imported in a nicer way for ESM users. The default export is left
-// as the entire namespace (module.exports) and updates when this function is
-// called so that APMs and other behavior are supported.
-NativeModule.prototype.syncExports = function() {
+  // Provide named exports for all builtin libraries so that the libraries
+  // may be imported in a nicer way for ESM users. The default export is left
+  // as the entire namespace (module.exports) and updates when this function is
+  // called so that APMs and other behavior are supported.
+  syncExports() {
     const names = this.exportKeys;
     if (this.module) {
       for (let i = 0; i < names.length; i++) {
@@ -272,9 +256,9 @@ NativeModule.prototype.syncExports = function() {
                               getOwn(this.exports, exportName, this.exports));
       }
     }
-};
+  }
 
-NativeModule.prototype.compile = function() {
+  compileForInternalLoader() {
     if (this.loaded || this.loading) {
       return this.exports;
     }
@@ -296,7 +280,37 @@ NativeModule.prototype.compile = function() {
 
     moduleLoadList.push(`NativeModule ${id}`);
     return this.exports;
+  }
+}
+
+// Think of this as module.exports in this file even though it is not
+// written in CommonJS style.
+const loaderExports = {
+  internalBinding,
+  NativeModule,
+  require: nativeModuleRequire
 };
 
-// This will be passed to internal/bootstrap/node.js.
+function nativeModuleRequire(id) {
+  if (id === loaderId) {
+    return loaderExports;
+  }
+
+  const mod = NativeModule.map.get(id);
+  // Can't load the internal errors module from here, have to use a raw error.
+  // eslint-disable-next-line no-restricted-syntax
+  if (!mod) throw new TypeError(`Missing internal module '${id}'`);
+  return mod.compileForInternalLoader();
+}
+
+// Allow internal modules from dependencies to require
+// other modules from dependencies by providing fallbacks.
+function requireWithFallbackInDeps(request) {
+  if (!NativeModule.map.has(request)) {
+    request = `internal/deps/${request}`;
+  }
+  return nativeModuleRequire(request);
+}
+
+// Pass the exports back to C++ land for C++ internals to use.
 return loaderExports;