DoCheck

A lifecycle hook that invokes a custom change-detection function for a directive, in addition to the check performed by the default change-detector on the input bindings for this directive usage in the parent template. Note that this hook is invoked even when the directive's own change detection is skipped (e.g., with the OnPush change detection strategy). Developers might use this hook to implement a custom change detection strategy for some of the inputs.

The default change-detection algorithm looks for differences by comparing bound-property values by reference across change detection runs. You can use this hook to check for and respond to changes by some other means.

When the default change detector detects changes to the directive's input bindings, it invokes ngOnChanges() if supplied, regardless of whether you perform additional change detection. Typically, you should not use both DoCheck and OnChanges to respond to changes on the same input.

The following snippet shows how a component can implement this interface to invoke it own change-detection cycle.

@Component({
        selector: 'my-cmp',
        template: `...`,
      })
      class MyComponent implements DoCheck {
        ngDoCheck() {
          // ...
        }
      }

For a more complete example and discussion, see Defining custom change detection.