Why we should use RxJs of() function?

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The reason why they’re using of() is because it’s very easy to use it instead of a real HTTP call.

In a real application you would implement getHeroes() like this for example:

getHeroes(): Observable<Hero[]> {
  return this.http.get(`/heroes`);
}

But since you just want to use a mocked response without creating any real backend you can use of() to return a fake response:

const HEROES = [{...}, {...}];

getHeroes(): Observable<Hero[]> {
  return of(HEROES);
}

The rest of your application is going to work the same because of() is an Observable and you can later subscribe or chain operators to it just like you were using this.http.get(...).

The only thing that of() does is that it emits its parameters as single emissions immediately on subscription and then sends the complete notification.

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