订阅未在角度2中定义? [英] subscribe is not defined in angular 2?

问题描述

我正在Angular 2中创建一个演示应用程序，并希望在我的组件中控制台 params ['id'] ，id来自查询参数.

I am creating a demo app in Angular 2 and want to console params['id'] in my component, id is coming from query params.

要实现这一点，我需要在组件中执行以下操作:

To achieve this I am doing this in my component:

ngOnInit(): void {
     this.route.params
          .switchMap(
           (params: Params) => 
                this.heroService.getHero(+params['id']);
                console.log("ID :",params['id'])
           ).subscribe(hero => this.hero = hero);
    };

但是我得到了这个错误:

But i got this error:

core.umd.js:3491 EXCEPTION: Uncaught (in promise): Error: Error in :0:0 caused by: params is not defined
ReferenceError: params is not defined

请提出我需要做些什么来控制参数的ID?

Please suggest what I will have to do to console the param's id ?

推荐答案

您需要具有 {} 才能向箭头函数添加更多语句.我想您可能想做:

You need to have {} to add more statements to an arrow function. I think you might want to do:

    ngOnInit(): void {
         this.route.params
              .switchMap((params: Params) => {
  console.log("ID :",params['id']));
  return this.heroService.getHero(+params['id']);
  }) .subscribe(hero => this.hero = hero);
};

为什么要回来?

switchmap返回的Observable在 subscribe 函数中进行了订阅.如果是箭头功能()=>声明等同于()=> {return statement;}

The Observable that is returned by switchmap is subscribed in subscribe function. In case of arrow functions ()=>statment is equivalent to ()=>{return statement;}

当您添加其他语句并使用花括号时，您需要添加缺失的收益.

When you add an additional statement and use brace you need to add the missing return.

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