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main.ts

index.html

import { bootstrapApplication } from '@angular/platform-browser';
import { Component, Input } from '@angular/core';

@Component({
  selector: 'child-cmp',
  standalone: true,
  template: `
    <p>Child received: {{ text }}</p>
    <p>Last change: {{ lastPrev || '∅' }} -> {{ lastCurr || '∅' }}</p>
  `
})
export class Child {
  @Input() text = '';
  lastPrev = null;
  lastCurr = null;
  ngOnChanges(changes) {
    const c = changes['text'];
    if (c) {
      this.lastPrev = c.previousValue ?? null;
      this.lastCurr = c.currentValue ?? null;
    }
  }
}

@Component({
  selector: 'app-root',
  standalone: true,
  imports: [Child],
  template: `
    <h3>OnChanges</h3>
    <label>Text: <input #i (input)="text=i.value" placeholder="Type here..."></label>
    <child-cmp [text]="text"></child-cmp>
  `
})
export class App {
  text = '';
}

bootstrapApplication(App);

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Angular Lifecycle - OnChanges</title>
</head>
<body>
  <app-root></app-root>
</body>
</html>