window-ref.ts 里的 isBrowser API,封装的是 Angular 标准 API,isPlatformBrowser: 来自 @angular/common: isBrowser(): boolean { // TODO(#11133): Remove condition when platformId will be always provided return this.platformId ? isPlatformBrowser(this.platformId) : typeof window !== 'undefined'; } 这是 @angular/common 里标准的 api: https:///api/common/isPlatformBrowser 然后单击进去之后,看不到具体的实现代码: @publicApi export declare function, 其用法解释:
var creates a new variable. declare is used to tell TypeScript that the variable has been created elsewhere. If you use declare, nothing is added to the JavaScript that is generated - it is simply a hint to the compiler. For example, if you use an external script that defines var externalModule, you would use declare var externalModule to hint to the TypeScript compiler that externalModule has already been set up export declare class Action{...} The class's real implementation is probably in somewhere else - maybe a .js file. declare 提示了 Action 的实际实现一定在另一个位置,很可能是某个 .js 文件里。 TypeScript 帮助文档里对 declare 关键字的解释:
TypeScript 的 declare 关键字,用于声明一个变量,其原始定义可能并不是来自一个 TypeScript 文件。
declare var myLibrary; The type that the TypeScript runtime will give to myLibrary variable is the any type. The problem here is that you won’t have Intellisense for that variable in design time but you will be able to use the library in your code. Another option to have the same behavior without using the declare keyword is just using a variable with the any type: var myLibrary: any; 报错:uncaught referenceError: myLibrary is not defined |
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