深度刨析@angular/platform-browser-dynamic

1. 前言

作为 angular 应用的入口模块，了解他的重要性是显而易见的！

2. angular 之 main.ts

main.ts 是这个样子的，下面我就去解开 platformBrowserDynamic 神秘面纱！

platformBrowserDynamic()
  .bootstrapModule(AppModule)
  .catch((err) => console.error(err));

3. 解析 platformBrowserDynamic

platformBrowserDynamic 源码位于platform-browser-dynamic.ts

首先我们来看一下接口定义

/**
 * @publicApi
 */
export declare const platformBrowserDynamic: (
  extraProviders?: StaticProvider[] | undefined
) => PlatformRef;

方法返回的是一个 PlatformRef, 可以接受一个或多个额外的 Providers.

先看一下返回值对象 PlatformRef, 这是 PlatformRef 的源码及介绍

Angular platform 是 Angular 在网页上的入口点。
每一 web 页面有且仅有一个 platform。所有的服务（如反射）都绑定在其 scope 内并共享给整个 Angular application。
当使用 Angular platform 创建平台时，页面的 platform 会隐式初始化
factory，例如’PlatformBrowser’，或者通过调用’createPlatform（）’函数显式调用。

/**
 * The Angular platform is the entry point for Angular on a web page.
 * Each page has exactly one platform. Services (such as reflection) which are common
 * to every Angular application running on the page are bound in its scope.
 * A page's platform is initialized implicitly when a platform is created using a platform
 * factory such as `PlatformBrowser`, or explicitly by calling the `createPlatform()` function.
 *
 * @publicApi
 */
export declare class PlatformRef {
  private _injector;
  private _modules;
  private _destroyListeners;
  private _destroyed;
  /**
   * Creates an instance of an `@NgModule` for the given platform.
   *
   * @deprecated Passing NgModule factories as the `PlatformRef.bootstrapModuleFactory` function
   *     argument is deprecated. Use the `PlatformRef.bootstrapModule` API instead.
   */
  bootstrapModuleFactory<M>(
    moduleFactory: NgModuleFactory<M>,
    options?: BootstrapOptions
  ): Promise<NgModuleRef<M>>;
  /**
   * Creates an instance of an `@NgModule` for a given platform.
   *
   * @usageNotes
   * ### Simple Example
   *
   * ```typescript
   * @NgModule({
   *   imports: [BrowserModule]
   * })
   * class MyModule {}
   *
   * let moduleRef = platformBrowser().bootstrapModule(MyModule);
   * ```
   *
   */
  bootstrapModule<M>(
    moduleType: Type<M>,
    compilerOptions?:
      | (CompilerOptions & BootstrapOptions)
      | Array<CompilerOptions & BootstrapOptions>
  ): Promise<NgModuleRef<M>>;
  private _moduleDoBootstrap;
  /**
   * Registers a listener to be called when the platform is destroyed.
   */
  onDestroy(callback: () => void): void;
  /**
   * Retrieves the platform {@link Injector}, which is the parent injector for
   * every Angular application on the page and provides singleton providers.
   */
  get injector(): Injector;
  /**
   * Destroys the current Angular platform and all Angular applications on the page.
   * Destroys all modules and listeners registered with the platform.
   */
  destroy(): void;
  get destroyed(): boolean;
  static ɵfac: i0.ɵɵFactoryDeclaration<PlatformRef, never>;
  static ɵprov: i0.ɵɵInjectableDeclaration<PlatformRef>;
}

packages\core\src\application_ref.ts

为给定平台创建“@NgModule”的实例。

bootstrapModule<M>(
    moduleType: Type<M>,
    compilerOptions: (CompilerOptions&BootstrapOptions)|
    Array<CompilerOptions&BootstrapOptions> = []): Promise<NgModuleRef<M>> {
  const options = optionsReducer({}, compilerOptions);
  return compileNgModuleFactory(this.injector, options, moduleType)
      .then(moduleFactory => this.bootstrapModuleFactory(moduleFactory, options));
}

NgModuleFactory 的创建过程, 重点是创建 R3NgModuleFactory

export function compileNgModuleFactory<M>(
  injector: Injector,
  options: CompilerOptions,
  moduleType: Type<M>
): Promise<NgModuleFactory<M>> {
  ngDevMode && assertNgModuleType(moduleType);

  const moduleFactory = new R3NgModuleFactory(moduleType);

  // All of the logic below is irrelevant for AOT-compiled code.
  if (typeof ngJitMode !== "undefined" && !ngJitMode) {
    return Promise.resolve(moduleFactory);
  }

  const compilerOptions = injector.get(COMPILER_OPTIONS, []).concat(options);

  // Configure the compiler to use the provided options. This call may fail when multiple modules
  // are bootstrapped with incompatible options, as a component can only be compiled according to
  // a single set of options.
  setJitOptions({
    defaultEncapsulation: _lastDefined(
      compilerOptions.map((opts) => opts.defaultEncapsulation)
    ),
    preserveWhitespaces: _lastDefined(
      compilerOptions.map((opts) => opts.preserveWhitespaces)
    ),
  });

  if (isComponentResourceResolutionQueueEmpty()) {
    return Promise.resolve(moduleFactory);
  }

  const compilerProviders = _mergeArrays(
    compilerOptions.map((o) => o.providers!)
  );

  // In case there are no compiler providers, we just return the module factory as
  // there won't be any resource loader. This can happen with Ivy, because AOT compiled
  // modules can be still passed through "bootstrapModule". In that case we shouldn't
  // unnecessarily require the JIT compiler.
  if (compilerProviders.length === 0) {
    return Promise.resolve(moduleFactory);
  }

  const compiler = getCompilerFacade({
    usage: JitCompilerUsage.Decorator,
    kind: "NgModule",
    type: moduleType,
  });
  const compilerInjector = Injector.create({ providers: compilerProviders });
  const resourceLoader = compilerInjector.get(compiler.ResourceLoader);
  // The resource loader can also return a string while the "resolveComponentResources"
  // always expects a promise. Therefore we need to wrap the returned value in a promise.
  return resolveComponentResources((url) =>
    Promise.resolve(resourceLoader.get(url))
  ).then(() => moduleFactory);
}

核心代码在 R3NgModuleFactory 的创建部分
packages\core\src\render3\ng_module_ref.ts

constructor(ngModuleType: Type<T>, public _parent: Injector|null) {
  super();
  const ngModuleDef = getNgModuleDef(ngModuleType);
  ngDevMode &&
      assertDefined(
          ngModuleDef,
          `NgModule '${stringify(ngModuleType)}' is not a subtype of 'NgModuleType'.`);

  this._bootstrapComponents = maybeUnwrapFn(ngModuleDef!.bootstrap);
  this._r3Injector = createInjectorWithoutInjectorInstances(
                         ngModuleType, _parent,
                         [
                           {provide: viewEngine_NgModuleRef, useValue: this}, {
                             provide: viewEngine_ComponentFactoryResolver,
                             useValue: this.componentFactoryResolver
                           }
                         ],
                         stringify(ngModuleType)) as R3Injector;

  // We need to resolve the injector types separately from the injector creation, because
  // the module might be trying to use this ref in its constructor for DI which will cause a
  // circular error that will eventually error out, because the injector isn't created yet.
  this._r3Injector._resolveInjectorDefTypes();
  this.instance = this.get(ngModuleType);
}

6. Angular 系列文章

最新更新以及更多 Angular 相关文章请访问 Angular 合集 | 鹏叔的技术博客

5. 参考文章

深度解析@angular/platform-browser-dynamic
angular 源码分析之 platformBrowserDynamic
Angular Platforms in depth. Part 1