Zone.js is a JavaScript library used in Angular to provide execution context and hooks into asynchronous operations. It allows Angular to track and manage the execution of asynchronous tasks, such as event handling, timers, promises, and XHR requests. Zone.js enables Angular to perform change detection and update the UI when asynchronous operations complete.

Here's an example to illustrate the use of Zone.js in Angular: 


import { Component } from '@angular/core';

@Component({
  selector: 'app-example',
  template: `
    <button (click)="simulateAsyncTask()">Simulate Async Task</button>
    <p>Status: {{ status }}</p>
  `
})
export class ExampleComponent {
  status: string = 'Not started';

  simulateAsyncTask() {
    this.status = 'Processing...';

    setTimeout(() => {
      // Simulating an asynchronous task completion
      this.status = 'Completed';
    }, 2000);
  }
}
In this Angular component, we have a button and a paragraph displaying the status of an asynchronous task. When the button is clicked, the `simulateAsyncTask()` method is called. Inside the method, we update the `status` property to indicate that the task is being processed. Then, we use the `setTimeout` function to simulate a delay of 2 seconds. Behind the scenes, Zone.js intercepts the `setTimeout` call and hooks into the asynchronous operation. It allows Angular to track the execution of the task and ensures that change detection is triggered when the task completes. When the timeout expires, the callback function is executed, and the `status` property is updated to indicate that the task is completed. As a result, the UI is automatically updated to reflect the new status. Conclusion : Zone.js provides Angular with a way to seamlessly integrate asynchronous operations into the change detection mechanism, enabling efficient updating of the UI when asynchronous tasks finish. It simplifies the handling of asynchronous code and ensures that Angular remains aware of changes happening within the asynchronous context.