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OnChanges

interface

A lifecycle hook that is called when any data-bound property of a directive changes. Define an ngOnChanges() method to handle the changes.

interface OnChanges {
  ngOnChanges(changes: SimpleChanges): void
}

See also

Methods

A callback method that is invoked immediately after the default change detector has checked data-bound properties if at least one has changed, and before the view and content children are checked.

ngOnChanges(changes: SimpleChanges): void

Parameters
changes SimpleChanges

The changed properties.

Returns

void

Usage notes

The following snippet shows how a component can implement this interface to define an on-changes handler for an input property.

@Component({selector: 'my-cmp', template: `...`})
class MyComponent implements OnChanges {
  // TODO(issue/24571): remove '!'.
  @Input()
  prop !: number;

  ngOnChanges(changes: SimpleChanges) {
    // changes.prop contains the old and the new value...
  }
}

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Licensed under the Creative Commons Attribution License 4.0.
https://angular.io/api/core/OnChanges