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How to detect when an @Input() value changes in Angular?

Actually, there are two ways of detecting and acting upon when an input changes in the child component in angular.

  • Use the ngOnChanges() lifecycle method.
  • Use input property setter.
  @Input() categoryId: string;
        
    ngOnChanges(changes: SimpleChanges) {
        
        this.doSomething(changes.categoryId.currentValue);
        // You can also use categoryId.previousValue and 
        // categoryId.firstChange for comparing old and new values
        
    }

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