merge two steams of data and do something different based on input

merge-two-steams-of-date

import { Component } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { Subject } from 'rxjs/Subject';

import 'rxjs/add/observable/interval';
import 'rxjs/add/operator/map';
import 'rxjs/add/observable/merge';
import 'rxjs/add/operator/startWith';
import 'rxjs/add/operator/scan';
import 'rxjs/add/operator/mapTo';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  clock: Observable<any>;

  clock$ = new Subject();

  constructor() {
    this.clock = Observable.merge(
      this.clock$.mapTo('hour'),
      Observable.interval(3000).mapTo('second')
    )
      .startWith(new Date().toString())
      .scan((accu: Date, current) => {
        const date = new Date(accu);

        if (current === 'second') {
          date.setSeconds(date.getSeconds() + 1);
        }
        // tslint:disable-next-line:one-line
        else if (current === 'hour') {
          date.setHours(date.getHours() + 1);
        }

        return date;
      });
  }
}