Make parallel calls http get or post calls in angular 2

Question

How to make parallel calls HTTP get or post calls in angular 2?

I have 2 service calls on the response of one callus have to make another call.
Could some suggest me how to call make these parallel calls with error handling scenarios?

Answer 1

If your service is Observable based instead of Promise you can do forkJoin. It runs all observable sequences in parallel.

For RxJS version < 6

import 'rxjs/add/observable/forkJoin';

Make sure to import forkJoin from rxjs library

Observable.forkJoin(myService.getCall(),
            myService.postCall(),
            ...)
            .subscribe((res) => {
              res[0] // this is first service call response,
              res[1] // this is second service call response
              ...
});

Or if you want it to be sequential do the first call and on complete call second.

myService.getCall().subscribe((response) => {
  // handle response
}, (error) => {
  // handle error here
}, () => {
  // this is complete block and it is triggered when obervable is complete
  myService.postCall();
}

EDIT: for RxJS 6 and above forkJoin has changed

Service:

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { forkJoin, Observable } from 'rxjs';

@Injectable()
export class MyService {

  constructor(private  http: HttpClient) {
  }

  getAndPost(): Observable<any> {
    return forkJoin(
      this.http.get('/api/get'),
      this.http.post('/api/post')
    );
  }
}

Component:

firstResponse: any;
secondResponse: any;

constructor(private myService: MyService) {
}

myFunction(): void {
  this.myService.getAndPost().subscribe((res) => {
    this.firstResponse = res[0],
    this.secondResponse = res[1]
  });
}