“map((response) => response.json())”和“map((response) =>{ response.json();})”之间的区别 [重复]

Question

这里是源代码：

export class PostComponent implements OnInit {

    posts: any[];

    constructor(private http: Http, private service: PostService) {
    }
    getAll1() {
    const url = 'http://jsonplaceholder.typicode.com/posts';
    this.http.get(url)
    .map((respone) => respone.json())
    .subscribe(posts => this.posts = posts );
    }  
  }

`

它工作正常，但是如果我为“respone.json”添加花括号，那么视觉标准输出代码会提示错误（见下文）。 添加大括号后的源代码如下：

export class PostComponent implements OnInit {

    posts: any[];

    constructor(private http: Http, private service: PostService) {
    }
    getAll1() {
    const url = 'http://jsonplaceholder.typicode.com/posts';
    this.http.get(url)
    .map((respone) => {respone.json();})
    .subscribe(posts => this.posts = posts );
    }  
  }

错误出现在最后一行的单词“this.posts”上，错误是：[ts] Type 'void' is notassignable to type 'any[]'。

为什么？

Answer 1

.map((respone) => respone.json())其实和这个是一样的：

.map((respone) => { return respone.json() })

而.map((respone) => { respone.json() }) 与此类似：

.map((respone) => { respone.json(); return undefined; })

因此，在您的第二个代码块中，respone.json() 刚刚被解除。