// Tutorial //

How To Use @HostBinding and @HostListener in Custom Angular Directives

Published on May 4, 2017 · Updated on July 12, 2021
Default avatar
By Alligator.io
Developer and author at DigitalOcean.
How To Use @HostBinding and @HostListener in Custom Angular Directives

Introduction

@HostBinding and @HostListener are two decorators in Angular that can be really useful in custom directives. @HostBinding lets you set properties on the element or component that hosts the directive, and @HostListener lets you listen for events on the host element or component.

In this article, you will use @HostBinding and @HostListener in an example directive that listens for a keydown event on the host.

Animated gif of text entered into an input as color changes with each character. The message spells out: A rainbow of colors.

It will set its text and border color to a random color from a set of a few available colors.

Prerequisites

To complete this tutorial, you will need:

This tutorial was verified with Node v16.4.2, npm v7.18.1, angular v12.1.1.

Using @HostBinding and @HostListener

First, create a new RainbowDirective.

This can be accomplished with @angular/cli:

  1. ng generate directive rainbow --skip-tests

This will add the new component to the app declarations and produce a rainbow.directive.ts file:

src/app/rainbow.directive.ts
import { Directive } from '@angular/core';

@Directive({
  selector: '[appRainbow]'
})
export class RainbowDirective {

  constructor() { }

}

Add @HostBinding and @HostListener:

src/app/rainbow.directive.ts
import { Directive, HostBinding, HostListener } from '@angular/core';

@Directive({
  selector: '[appRainbow]'
})
export class RainbowDirective {

  possibleColors = [
    'darksalmon',
    'hotpink',
    'lightskyblue',
    'goldenrod',
    'peachpuff',
    'mediumspringgreen',
    'cornflowerblue',
    'blanchedalmond',
    'lightslategrey'
  ];

  @HostBinding('style.color') color!: string;
  @HostBinding('style.border-color') borderColor!: string;

  @HostListener('keydown') newColor() {
    const colorPick = Math.floor(Math.random() * this.possibleColors.length);

    this.color = this.borderColor = this.possibleColors[colorPick];
  }

}

And the directive can be used on elements like this:

src/app/app.component.html
<input type="text" appRainbow />

Our Rainbow directive uses two @HostBinding decorators to define two class members, one that’s attached to the host’s style.color binding and the other to style.border-color.

You can also bind to any class, property, or attribute of the host.

Here are a few more examples of possible bindings:

  • @HostBinding('class.active')
  • @HostBinding('disabled')
  • @HostBinding('attr.role')

The @HostListener with the 'keydown' argument listens for the keydown event on the host. We define a function attached to this decorator that changes the value of color and borderColor, and our changes get reflected on the host automatically.

Conclusion

In this article, you used @HostBinding and @HostListener in an example directive that listens for a keydown event on the host.

If you’d like to learn more about Angular, check out our Angular topic page for exercises and programming projects.


Want to learn more? Join the DigitalOcean Community!

Join our DigitalOcean community of over a million developers for free! Get help and share knowledge in our Questions & Answers section, find tutorials and tools that will help you grow as a developer and scale your project or business, and subscribe to topics of interest.

Sign up
About the authors
Default avatar
Developer and author at DigitalOcean.

Still looking for an answer?

Was this helpful?
Leave a comment

This textbox defaults to using Markdown to format your answer.

You can type !ref in this text area to quickly search our full set of tutorials, documentation & marketplace offerings and insert the link!