Add element to Observable array typescript

Question

I have an angular 2 Component which make use of service that is getting data from rest api.

import { OnInit, Component } from '@angular/core';
import { Hero } from './hero';
import { HeroService } from './hero.service2';
import { Observable } from 'rxjs';


@Component({
    selector: 'my-list',
    templateUrl: 'app/hero-list.component.html',
})
export class HeroListComponent implements OnInit {
  errorMessage: string;
  heroes: Observable<Hero[]>;
  mode = 'Observable';

  constructor (
      private heroService: HeroService
  ) {}

  ngOnInit() { this.getHeroes(); }

  getHeroes() {
    this.heroes = this.heroService.getHeroes()
  }

  addHero (name: string) {
    if (!name) { return; }

    this.heroService.addHero(name)
                     .subscribe(
                       hero  => this.getHeroes()
                     );
  }
}

How can i improve addHero ? Because right now it looks like very inefficient. I would like to just add hero that is returned by this.heroService.addHero() to heroes Observable. How do i do that?

ABabin · Accepted Answer · 2016-08-26 16:51:17Z

There is no point assigning the Observable that heroService.getHeroes() returns to the hereoes property, and reassigning it every time you add a Hero doesn't make much sense either.

Without editing HeroService, you can improve the HeroListComponent like so:

heroes: Hero[];

  ngOnInit() {
    this.getHeroes();
  }

  getHeroes() {
    this.heroService.getHeroes().subscribe(heroArray => {
      //The response from getHeroes() is a array of Hero so assign 
      //  that directly to heroes property
      this.heroes = heroArray;
    });
  }

  addHero (name: string) {
    //Makes sure name isn't an empty string. Typescript compiler will catch everything else.
    if (name) {
      this.heroService.addHero(name).subscribe(hero => {
        //I assume the response from the addHero Observable is a Hero object
        this.heroes.push(hero);
      });
    } else {
      //Notify console when passed empty string.
      console.error('Error! addHero was passed an empty string!');
    }
  }

You could probably make further improvements by editing your HeroService, but this is a good start.

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