{{myArray}} now updates in the view as of beta.16

Question

Change detection has changed.

Before beta.16, if your view contains {{myArray}}, that binding won't update if you don't modify the array reference. E.g., if you push() items onto the array, the view won't update to show the new item. The explanation is (well, was) that because the array reference didn't changed, Angular change detection doesn't reevaluate the binding. This beta.15 plunker demonstrates this behavior.

As of beta.16 (and hence RC.1), things are different. The {{myArray}} binding will now update even if the array reference hasn't changed! See this RC.1 plunker.

I looked at the ChangeLog for beta.16, and I don't see anything that would account for this change in behavior (but maybe I missed something). Does anyone know what caused this change, and what else might be affected?

Plunker code:

@Component({
  selector: 'child',
  template: `<p>child: {{arr}}`
})
export class Child {
  @Input() arr;
}
@Component({
  selector: 'my-app',
  template: `{{title}} <p>parent: {{arr}}
    <button (click)="modifyArray()">modify array</button>
    <child [arr]="arr"></child>`,
  directives: [Child]
})
export class AppComponent {
  title = "Angular 2 beta.15";  // or "Angular 2 RC.1", as appropriate
  arr = 'one two three'.split(' ');
  modifyArray() {
    this.arr.push('another');
    console.log(this.arr);
  }
}

the beta.15 plnkr shows RC1, is it the wrong link? – Michael Kang May 18 '16 at 13:34 — Michael Kang, May 18 '16 at 13:34
@pixelbits, I resaved the plunker, try it now. – Mark Rajcok May 18 '16 at 13:38 — Mark Rajcok, May 18 '16 at 13:38

yurzui · Accepted Answer · 2016-05-18T15:19:32.850

4

I think that code related with DetectChanges is changed (ChangeDetector.detectChangesInRecordsInternal beta.15 vs View.detectChangesInternal rc.1). You can see it in pictures.

Beta.15 stack

As you can see there is a comparison of arrays

RC.1 stack

Then we can see comparison of expression(string) and they're different. So angular rc.1 will update view.

May it will help you :)

edited May 18 '16 at 15:19

answered May 18 '16 at 15:13

yurzui

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Thanks. I suspected that Angular is now comparing the result of the `{{expression}}`, rather than the arrays, but you proved/showed it. Where did you set a breakpoint to take the screenshots? – Mark Rajcok May 18 '16 at 15:41
Firstly i just set debugger in front of this.arr.push('another'). Then i went here https://github.com/angular/angular/blob/master/modules/%40angular/core/src/application_ref.ts#L301 – yurzui May 18 '16 at 15:49

{{myArray}} now updates in the view as of beta.16

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