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Miguel Moura
Miguel Moura

Reputation: 39444

Initialise variables (observables included) on Angular: Constructor, Declaration or ngOnInit?

I have the following Angular component:

export class ListComponent implements OnInit {

  showComments: boolean = false;

  posts$: Observable<PostModel[]>;

  constructor(private postService: PostService) { }

  ngOnInit() {

    this.posts$ = this.getPosts();

  }

  getPosts(): Observable<PostModel[]> {

    return this.postService.getRecentPosts();

  }

}

Should I define posts$ inside the constructor?

That about showComments default value? Inside ngOnInit too?

If not, when should I use ngOnInit?

Upvotes: 0

Views: 151

Answers (1)

youssef elhayani
youssef elhayani

Reputation: 745

Constructor usage in Angular: In Angular, the constructor is used for injecting dependencies into the component class. Nothing much. And keep the constructor as simple as possible

ngOnInit() method usage in Angular: Angular calls ngOnInit when it finishes creating a component DOM. And we will use constructors to inject all required dependencies and processed input bindings.

It’s a common practice to use ngOnInit to do actual work even though the logic doesn’t depend on DI, DOM or input bindings.

Upvotes: 1

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