What are the possible data update scenarios for change detection?

The change detection works in the following scenarios where the data changes needs to update the application HTML.

  1. Component initialization: While bootstrapping the Angular application, Angular triggers the ApplicationRef.tick() to call change detection and View Rendering.

  2. Event listener: The DOM event listener can update the data in an Angular component and trigger the change detection too.

    @Component({
    selector: 'app-event-listener',
    template: ` <button (click)="onClick()">Click</button>
    {{ message }}`,
    })
    export class EventListenerComponent {
    message = '';
    onClick() {
    this.message = 'data updated';
    }
    }
  3. HTTP Data Request: You can get data from a server through an HTTP request

    data = 'default value';
    constructor(private httpClient: HttpClient) {}
    ngOnInit() {
    this.httpClient.get(this.serverUrl).subscribe(response => {
    this.data = response.data; // change detection will happen automatically
    });
    }
  4. Macro tasks setTimeout() or setInterval(): You can update the data in the callback function of setTimeout or setInterval

    data = 'default value';
    ngOnInit() {
    setTimeout(() => {
    this.data = 'data updated'; // Change detection will happen automatically
    });
    }
  5. Micro tasks Promises: You can update the data in the callback function of promise

    data = 'initial value';
    ngOnInit() {
    Promise.resolve(1).then(v => {
    this.data = v; // Change detection will happen automatically
    });
    }
  6. Async operations like Web sockets and Canvas: The data can be updated asynchronously using WebSocket.onmessage() and Canvas.toBlob().


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Made by Michael Sakhniuk

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