@happy-dom/jest-environment

About

A JSDOM alternative with focus on performance.

Happy DOM aim to support the most common functionality of a web browser.

This package makes it possible to use Happy DOM with Jest.

DOM Features

• Custom Elements (Web Components)

• Shadow Root (Shadow DOM)

• Mutation Observer

• Tree Walker

• Fetch

And much more..

Works With

• Google LitHTML

• Google LitElement

• React

• Angular

• Vue

Installation

npm install @happy-dom/jest-environment --save-dev

Setup

Jest uses JSDOM as test environment by default. In order to tell Jest to use a different environment we will either have to set a CLI attribute, define it in "package.json" or add a property to your Jest config file.

CLI

1. Edit your "package.json" file.

2. Add "--env=@happy-dom/jest-environment" as an attribute to your Jest command.

   {
       "scripts": {
           "test": "jest --env=@happy-dom/jest-environment"
       }
   }
   

3. Save the file.

In "package.json"

1. Edit your "package.json" file.

2. Add the following to it:

   {
       "jest": {
           "testEnvironment": "@happy-dom/jest-environment"
       }
   }
   

3. Save the file.

Configuration File

1. Edit your Jest config file (usually jest.config.js)

2. Add the following to it:

   {
     "testEnvironment": "@happy-dom/jest-environment"
   }
   

3. Save the file.

Additional Features

Happy DOM exposes two functions that may be useful when testing asynchrounous code.

whenAsyncComplete()

Returns a Promise that is resolved when all async tasks has been completed.

describe('scrollToTop()', () => {
    it('scrolls to top using the built in browser animation', async () => {
        element.scrollToTop();

        // Waits for asynchronous tasks like setTimeout(), requestAnimationFrame() etc. to complete
        await happyDOM.whenAsyncComplete();

        expect(document.documentElement.scrollTop).toBe(0);
    });
});

cancelAsync()

This method will cancel all running async tasks.

describe('runAnimation()', () => {
    it('runs animation', () => {
        element.runAnimation();

        // Cancels all asynchronous tasks like setTimeout(), requestAnimationFrame() etc.
        happyDOM.cancelAsync();

        expect(element.animationCompleted).toBe(true);
    });
});

Performance

Operation	JSDOM	Happy DOM
Import / Require	333 ms	45 ms
Parse HTML	256 ms	26 ms
Serialize HTML	65 ms	8 ms
Render custom element	214 ms	19 ms
querySelectorAll('tagname')	4.9 ms	0.7 ms
querySelectorAll('.class')	6.4 ms	3.7 ms
querySelectorAll('[attribute]')	4.0 ms	1.7 ms
querySelectorAll('[class~="name"]')	5.5 ms	2.9 ms
querySelectorAll(':nth-child(2n+1)')	10.4 ms	3.8 ms

See how the test was done here