How send request via interval operator?

Question

I try send http-request. I use angular 2 and rxjs library. I need send a request with a period of 5 seconds.

At first i import operator and use it follow:

import { Injectable } from '@angular/core'; import { HttpClient } from '@angular/common/http'; import { Observable } from 'rxjs/Observable'; // import { interval } from 'rxjs/observable/interval'; import 'rxjs/add/observable/interval'; @Injectable() export class TasksService { constructor(private http: HttpClient) { }; getUserTasks(userId): Observable<any> { return this.http.interval(5000).get('http://127.0.0.1:8000/app_tasks/user_tasks?user_id=' + userId); }; }

Secondly i subscribe in component:

ngOnInit() { let userId = 1; this.getUserTasks(userId); } private getUserTasks(userId): void { this.tasksService.getUserTasks(userId).subscribe( data => { this.userTasks = JSON.parse(data); console.log('userTasks', this.userTasks); } ) };

But consoe display follow error message:

ERROR in src/app/services/tasks.service.ts(16,21): error TS2339: Property 'interval' does not exist on type 'HttpClient'.

Mark van Straten · Accepted Answer · 2017-12-12 09:52:10Z

Interval is a creator function for an Observable, not HttpClient. I would try the following:

Observable.interval(5000) .switchMap(_ => this.http.get('http://127.0.0.1:8000/app_tasks/user_tasks?user_id=' + userId)

By using .switchMap you will abandon the previous http.get result if a new interval is hit before your previous request returns (5 seconds, hope that does not happen).

Denis Savenko · Accepted Answer · 2018-03-26 04:18:01Z

I think on Angular 4+ you should use IntervalObservable for this. You can read more about version changes on this old question (Angular2+ http at an interval) or use right answer @Ploppy https://stackoverflow.com/a/40285206/5319874

krystianpe · Accepted Answer · 2018-03-26 20:45:49Z

According to accepted answer. switchMap will not be the best idea if request takes more than 5 seconds. As alternative I'd rather suggest exhaustMap:

Observable.interval(5000) .exhaustMap(_ => this.http.get(`http://127.0.0.1:8000/app_tasks/user_tasks?user_id=${userId}`)

It will not cancel pending request after 5 seconds but ignore any request until pending request either fails or returns value. But it depends on your case.

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