ngOnChanges() ( OnChanges ) is called when a value bound to an input has changed so you can run custom code when an input has changed. ngDoCheck() ( DoCheck ) is called when change detection runs so you can implement your custom change detection action.

What is ngDoCheck?

ngDoCheck() is called whenever change detection is run. ngDoCheck() is called immediately after ngOnChanges() and ngOnInit() Notice how our ChildComponent implements an OnPush change detection strategy.

How many times ngDoCheck called?

Why is the DoCheck hook called twice? So far I understand, DoCheck is called for every change detection.