Angular 2 OpaqueToken与Angular 4 InjectionToken [英] Angular 2 OpaqueToken vs Angular 4 InjectionToken

问题描述

InjectionToken是在Angular 4中引入的，OpaqueToken被标记为已弃用.

InjectionToken was introduced in Angular 4 and OpaqueToken was marked as deprecated.

根据手册，应该用作

const anyToken = new InjectionToken('any');

用于非类型化令牌，并为

for untyped token, and as

const numberToken = new InjectionToken<number>('number');

用于输入令牌.

但是，键入的令牌在注入时仍然可以注入并以其他类型使用，TypeScript可以接受，不是吗?

However, typed token still can be injected and used with different type when it is injected, TypeScript will be ok with this, won't it?

constructor(@Inject(numberToken) any, @Inject(numberToken) string: string) { ... }

InjectionToken应该如何从TypeScript类型系统中受益?

How is InjectionToken supposed to benefit from TypeScript type system?

如果这两个之间没有实际区别，为什么不推荐使用OpaqueToken?

Why was OpaqueToken deprecated if there's no practical difference between those two?

推荐答案

基于InjectionToken的内部用法，例如，

Based on the internal usage of InjectionToken, for example, here, I assume that InjectionToken gives you type checking benefit when getting a dependency through injector instance:

import {Component, InjectionToken, Injector} from "@angular/core";

interface AppConfig {
    name: string;
}

let APP_CONFIG = new InjectionToken<AppConfig>('app.config');
let appConfig: AppConfig = {name: 'Cfg'};

@Component({
    ...
    providers: [{provide: APP_CONFIG, useValue: appConfig}]
})
export class TestComponent {
    constructor(injector: Injector) {
        const config = injector.get(APP_CONFIG);
        config.s = 'd';
            ^^^^^ - Error:(14, 16) TS2339:Property 's' does not exist on type 'AppConfig'.
    }
}

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