返回一个空的Observable [英] Return an empty Observable

问题描述

函数more()应该从获取请求中返回Observable

The function more() is supposed to return an Observable from a get request

export class Collection{

    public more = (): Observable<Response> => {
       if (this.hasMore()) {

         return this.fetch();
       }
       else{
         // return empty observable
       }
    }

    private fetch = (): Observable<Response> => {
       return this.http.get('some-url').map(
          (res) => {
              return res.json();
          }
       );
    }
}

在这种情况下，我只能在hasMore()为true的情况下执行请求，否则在subscribe()函数subscribe is not defined上收到错误，如何返回空的可观察值?

In this case I can only do a request if hasMore() is true, else I get an error on subscribe() function subscribe is not defined, how can I return an empty observable?

this.collection.more().subscribe(
   (res) =>{
       console.log(res);
   },
   (err) =>{
       console.log(err);
   }
)

更新

在RXJS 6中

Update

In RXJS 6

import { EMPTY } from 'rxjs'

return EMPTY; 

推荐答案

对于打字稿，您可以指定空的Observable的通用参数，如下所示:

For typescript you can specify generic param of your empty observable like this:

import 'rxjs/add/observable/empty' 

Observable.empty<Response>();

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