The ngOnChanges lifecycle hook is failing to execute

I've encountered an issue where ngOnChanges is not being called when updating a component property. To see the problem and my attempted solutions, please check out the StackBlitz linked below:

https://stackblitz.com/edit/angular-becgjq

Update: corrected link to access code details.

Highlighted code snippet

ngOnInit() {
    const testButton1 = document.getElementById('test-button1');
    testButton1.addEventListener('click', function() {
      console.log('about to set this.value');
      console.log(this.value);
      this.value = 'value set by button 1';
    }.bind(this));
    const testButton2 = document.getElementById('test-button2');
    testButton2.addEventListener('click', this.testButtonCallback2(this), false);
    const testButton3 = document.getElementById('test-button3');
    testButton3.addEventListener('click', this.testButtonCallback3.bind(this), false);
  }

  ngOnChanges() {
    console.log('ngOnChanges was called');
  }

  testButtonCallback2(outerThis) {
    return function() {
      console.log('about to set this.value');
      console.log(outerThis.value);
      outerThis.value = 'value is set by callback2';
    }
  }

  testButtonCallback3() {
    console.log('about to set this.value');
    console.log(this.value);
    this.value = 'value is set by callback3';
    this.changeDetectorRef.detectChanges();
  }

Answer №1

Take a look at the official documentation.

Angular triggers its ngOnChanges() method whenever it identifies modifications to input properties of the component (or directive).

Your component does not have any input variables, so ngOnChanges will not be executed.

Furthermore, it is recommended to utilize Angular's provided methods. I suggest following the tutorial. For example, avoid adding event listeners with addEventListener, and use (click) in your template like this instead:

<button (click)="testButtonCallback()">Test Button</button>
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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