13 December, 2017

What is the right way to wait for data in Angular?

I have a child-component CheckboxListComponent which shows a list of checkboxes. The list is populated in ngOnInit through a webservice-call which takes more or less time. It also has a function setEntryChecked to set a specific item to checked. When foo() is called before the CheckboxListComponent has it's data the call was lost or has no effect. My solution is to wait for the result to be available with await this.listSubject.first().toPromise(). Is there a better way to do this in TypeScript?

export class MainComponent {
  @ViewChild('checkboxList') checkboxListComponent: CheckboxListComponent;
  foo() {
     this.checkboxListComponent.setEntryChecked(..., true);

export class CheckboxListComponent implements OnInit {
  list: [];
  private listSubject = new Subject();

  async ngOnInit() {
    try {
      this.list = await this.dataService.get('url');
    } catch (err) {
    this.listSubject = undefined;

  async setEntryChecked(name: string, isChecked: boolean) {
     // wait for the list to be initialized
     if (this.listSubject) {
       await this.listSubject.first().toPromise();
     // make the item checked