Constructor vs ngOnInit

[crsanti]

In sample 01 Displaying Data the AppComponent is initializing the customers collection in the constructor() and customer in ngOnInit:

...
export class AppComponent implements OnInit {
  title = 'Displaying Data Demo';
  private customers: Customer[];
  customer: Customer;

  constructor() {
    this.customers = [
      new Customer('Jai', 'Sal', '25 June 1981',
      'http://vignette2.wikia.nocookie.net/disney/images/...'),
      new Customer('Fer', 'Sal', '25 November 1984'),
      new Customer('Lau', 'Sal', '04 March 2013')
    ];
  }

  ngOnInit() {
    this.customer = this.customers[0];
  }

but in sample 02 Displaying Collections customers assignation was moved to ngOnInit:

...
export class AppComponent implements OnInit {
  title = 'Displaying Collections Demo';
  customers: Customer[];

  constructor() {
  }

  ngOnInit() {
    this.customers = [
      new Customer('Jai', 'Sal', '25 June 1981',
      'http://vignette2.wikia.nocookie.net/disney/images/...'),
      new Customer('Fer', 'Sal', '25 November 1984',
      'http://vignette4.wikia.nocookie.net/disney/images/...'),
      new Customer('Lau', 'Sal', '04 March 2013',
      'https://vignette2.wikia.nocookie.net/pixar/images/...')
    ];
  }
}

How does it sound to keep the initialization only in one method? I think constructor() is more appropiated to initialize variables (later, given the right moment we could explain when use ngOnInit over constructor).

[JaimeSalas]

That is on purpose, the good practice in Angular is to get initialized using the lving hook events of component. Basically the constructor is only used for dependency injection.

[crsanti]

Ok, I got it ;)