flatMap.example.ts

import { Component, OnInit } from '@angular/core';
import { Http } from '@angular/http';
import { Observable } from 'rxjs/Observable';

import 'rxjs/Rx';
import 'rxjs/add/operator/mergeMap';

@Component({
  selector: 'example-flatMap',
  templateUrl: 'flat-map.component.html'
})

export class FlatMapComponent implements OnInit {
  
  dataA: Array<Object> = [];
  dataB: Array<number> = [];
  dataC: Array<string> = [];

  constructor(public http: Http) {}

  ngOnInit() {
    this.http.get('http://www.server.com/dataA')
      .map(res => res.json())
      .flatMap(res => {
        this.dataA = res;
        return  this.http.get('http://www.server.com/dataB').map(res => res.json());
      })
      .flatMap(res => {
        this.dataB = res;
        return this.http.get('http://www.server.com/dataC').map(res => res.json())
      })
      .subscribe(res => this.dataC = res);
  }
}