Getting Started

Install Jest using your favorite package manager:

npm install --save-dev jest

yarn add --dev jest

pnpm add --save-dev jest

Let's get started by writing a test for a hypothetical function that adds two numbers. First, create a sum.js file:

function sum(a, b) {
  return a + b;
}
module.exports = sum;

Then, create a file named sum.test.js . This will contain our actual test:

const sum = require('./sum');

test('adds 1 + 2 to equal 3', () => {
  expect(sum(1, 2)).toBe(3);
});

Add the following section to your package.json :

{
  "scripts": {
    "test": "jest"
  }
}

Finally, run yarn test or npm test and Jest will print this message:

PASS  ./sum.test.js
✓ adds 1 + 2 to equal 3 (5ms)

You just successfully wrote your first test using Jest!

This test used expect and toBe to test that two values were exactly identical. To learn about the other things that Jest can test, see Using Matchers .

Running from command line ​

You can run Jest directly from the CLI (if it's globally available in your PATH , e.g. by yarn global add jest or npm install jest --global ) with a variety of useful options.

Here's how to run Jest on files matching my-test , using config.json as a configuration file and display a native OS notification after the run:

jest my-test --notify --config=config.json

If you'd like to learn more about running jest through the command line, take a look at the Jest CLI Options page.

Additional Configuration ​

Generate a basic configuration file ​

Based on your project, Jest will ask you a few questions and will create a basic configuration file with a short description for each option:

npm init jest@latest

yarn create jest@latest

pnpm create jest@latest

Using Babel ​

To use Babel , install required dependencies:

npm install --save-dev babel-jest @babel/core @babel/preset-env

yarn add --dev babel-jest @babel/core @babel/preset-env

pnpm add --save-dev babel-jest @babel/core @babel/preset-env

Configure Babel to target your current version of Node by creating a babel.config.js file in the root of your project:

module.exports = {
  presets: [['@babel/preset-env', {targets: {node: 'current'}}]],
};

The ideal configuration for Babel will depend on your project. See Babel's docs for more details.

module.exports = api => {
  const isTest = api.env('test');
  // You can use isTest to determine what presets and plugins to use.

  return {
    // ...
  };
};

module.exports = {
  transform: {},
};

Using webpack ​

Jest can be used in projects that use webpack to manage assets, styles, and compilation. webpack does offer some unique challenges over other tools. Refer to the webpack guide to get started.

Using Vite ​

Jest can be used in projects that use vite to serve source code over native ESM to provide some frontend tooling, vite is an opinionated tool and does offer some out-of-the box workflows. Jest is not fully supported by vite due to how the plugin system from vite works, but there are some working examples for first-class jest integration using vite-jest , since this is not fully supported, you might as well read the limitation of the vite-jest . Refer to the vite guide to get started.

Using Parcel ​

Jest can be used in projects that use parcel-bundler to manage assets, styles, and compilation similar to webpack. Parcel requires zero configuration. Refer to the official docs to get started.

Using TypeScript ​

Via babel ​

Jest supports TypeScript, via Babel. First, make sure you followed the instructions on using Babel above. Next, install the @babel/preset-typescript :

npm install --save-dev @babel/preset-typescript

yarn add --dev @babel/preset-typescript

pnpm add --save-dev @babel/preset-typescript

Then add @babel/preset-typescript to the list of presets in your babel.config.js .

module.exports = {
  presets: [
    ['@babel/preset-env', {targets: {node: 'current'}}],
    '@babel/preset-typescript',
  ],
};

However, there are some caveats to using TypeScript with Babel. Because TypeScript support in Babel is purely transpilation, Jest will not type-check your tests as they are run. If you want that, you can use ts-jest instead, or just run the TypeScript compiler tsc separately (or as part of your build process).

Via ts-jest ​

ts-jest is a TypeScript preprocessor with source map support for Jest that lets you use Jest to test projects written in TypeScript.

npm install --save-dev ts-jest

yarn add --dev ts-jest

pnpm add --save-dev ts-jest

In order for Jest to transpile TypeScript with ts-jest , you may also need to create a configuration file.

Type definitions ​

There are two ways to have Jest global APIs typed for test files written in TypeScript.

You can use type definitions which ships with Jest and will update each time you update Jest. Install the @jest/globals package:

npm install --save-dev @jest/globals

yarn add --dev @jest/globals

pnpm add --save-dev @jest/globals

And import the APIs from it:

import {describe, expect, test} from '@jest/globals';
import {sum} from './sum';

describe('sum module', () => {
  test('adds 1 + 2 to equal 3', () => {
    expect(sum(1, 2)).toBe(3);
  });
});

Or you may choose to install the @types/jest package. It provides types for Jest globals without a need to import them.

npm install --save-dev @types/jest

yarn add --dev @types/jest

pnpm add --save-dev @types/jest

Using ESLint ​

Jest can be used with ESLint without any further configuration as long as you import the Jest global helpers ( describe , it , etc.) from @jest/globals before using them in your test file. This is necessary to avoid no-undef errors from ESLint, which doesn't know about the Jest globals.

If you'd like to avoid these imports, you can configure your ESLint environment to support these globals by adding the jest environment: