HostListener Decorators in Angular 17

Decorators are declarative functions in Angular that are used to change classes, methods, or properties. They serve as a source of metadata that instructs Angular on how to handle a class.

What is HostListener Decorator?

The @HostListener decorator in Angular provides a convenient way to listen for events on the host element of a component. It allows to define event handlers directly within the component class. In order to listen to events on the host element of the directive or component, one uses Angular's @HostListener decorator. This decorator function takes an event name as a parameter. The related function is called by the host element when that event is fired.

Syntax :

@component({
    selector: ['appExampleDirective']
})
export class ExampleDirective {
    @HostListener('event') methodName() {
        //code to execute  when the event  occurs
    }
}

Features of HostListener

• Better Type Inference: Angular 17 reduce the requirement for manual type annotations by providing improved type inference for event arguments in @HostListener decorators.
• Event Modifier Support: To provide more streamlined event processing, it might be improved to include event modifiers like .prevent, .stop in @HostListener decorators.
• Dynamic Event Binding: Using @HostListener, Angular 17 may bring the capability to dynamically bind event listeners, opening up more adaptable event handling scenarios.
• Conditional Event Handling: Depending on specific requirements inside the component or directive, modifications may be made to enable conditional event handling.

Uses of HostListener

• Event Parameterization: Event data like coordinates, target element, key codes, etc. may be accessed by capturing event objects with @HostListener and giving them as parameters to event handler functions.
• Type Safety: TypeScript's @HostListener reduces the possibility of runtime errors by enabling you to declare the type of event objects being supplied to the event handler methods.
• Integration with Directives: To attach event listeners to host elements and define associated behavior based on user interactions or other events, @HostListener is frequently used within directives.
• Dynamic Event Binding: To handle events more adaptably, @HostListener can be used to dynamically bind event listeners based on component state or other criteria.

Steps to Create Angular Project

Step 1: Create the angular project using the following command.

ng new app_name

• Which stylesheet format would you like to use ? - CSS
• Do you want to enable Server-Side Rendering (SSR) and Static Site Generation (SSG/Prerendering) ? - yes .

Step 2: Open Your project and go to terminal to start the application.

ng serve

Folder Structure:

HostListener Decorators in Angular 17

Dependencies:

"dependencies": {
    "@angular/animations": "^17.3.0",
    "@angular/common": "^17.3.0",
    "@angular/compiler": "^17.3.0",
    "@angular/core": "^17.3.0",
    "@angular/forms": "^17.3.0",
    "@angular/platform-browser": "^17.3.0",
    "@angular/platform-browser-dynamic": "^17.3.0",
    "@angular/router": "^17.3.0",
    "rxjs": "~7.8.0",
    "tslib": "^2.3.0",
    "zone.js": "~0.14.3"
  }

Example: This example shows the implementation of hostListners decorators.

HTML

<!-- app.component.html -->

<div style="text-align: left; 
    color: brown; background-color: yellowgreen">
    <h1>Welcome to learn about Decorators</h1>
</div>

<button [disabled]="buttonDisabled">Click me</button>

JavaScript

//app.component.ts

import { Component, HostListener } from '@angular/core';
import { RouterOutlet } from '@angular/router';

@Component({
    selector: 'app-root',
    standalone: true,
    imports: [RouterOutlet],
    templateUrl: './app.component.html',
    styleUrl: './app.component.css'
})
export class AppComponent {
    title = 'decorator';

    buttonDisabled = false;

    @HostListener('click', ['$event.target'])
    onClick(target: HTMLElement) {
        if (target.tagName === 'BUTTON') {
            this.toggleButton();
        }
    }

    toggleButton() {
        this.buttonDisabled = !this.buttonDisabled;
    }
}

Output :