---
id: getting-started
title: Getting Started
---

Install Jest using [`yarn`](https://yarnpkg.com/en/package/jest):

```bash
yarn add --dev jest
```

Or [`npm`](https://www.npmjs.com/package/jest):

```bash
npm install --save-dev jest
```

Note: Jest documentation uses `yarn` commands, but `npm` will also work. You can compare `yarn` and `npm` commands in the [yarn docs, here](https://yarnpkg.com/en/docs/migrating-from-npm#toc-cli-commands-comparison).

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

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

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

```javascript
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`:

```json
{
  "scripts": {
    "test": "jest"
  }
}
```

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

```bash
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](UsingMatchers.md).

## 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:

```bash
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](CLI.md) 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:

```bash
jest --init
```

### Using Babel

To use [Babel](https://babeljs.io/), install required dependencies via `yarn`:

```bash
yarn add --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:

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

_The ideal configuration for Babel will depend on your project._ See [Babel's docs](https://babeljs.io/docs/en/) for more details.

<details><summary markdown="span"><strong>Making your Babel config jest-aware</strong></summary>

Jest will set `process.env.NODE_ENV` to `'test'` if it's not set to something else. You can use that in your configuration to conditionally setup only the compilation needed for Jest, e.g.

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

  return {
    // ...
  };
};
```

> Note: `babel-jest` is automatically installed when installing Jest and will automatically transform files if a babel configuration exists in your project. To avoid this behavior, you can explicitly reset the `transform` configuration option:

```javascript
// jest.config.js
module.exports = {
  transform: {},
};
```

</details>

<details><summary markdown="span"><strong>Babel 6 support</strong></summary>

Jest 24 dropped support for Babel 6. We highly recommend you to upgrade to Babel 7, which is actively maintained. However, if you cannot upgrade to Babel 7, either keep using Jest 23 or upgrade to Jest 24 with `babel-jest` locked at version 23, like in the example below:

```
"dependencies": {
  "babel-core": "^6.26.3",
  "babel-jest": "^23.6.0",
  "babel-preset-env": "^1.7.0",
  "jest": "^24.0.0"
}
```

While we generally recommend using the same version of every Jest package, this workaround will allow you to continue using the latest version of Jest with Babel 6 for now.

</details>

### Using webpack

Jest can be used in projects that use [webpack](https://webpack.js.org/) to manage assets, styles, and compilation. webpack does offer some unique challenges over other tools. Refer to the [webpack guide](Webpack.md) to get started.

### Using parcel

Jest can be used in projects that use [parcel-bundler](https://parceljs.org/) to manage assets, styles, and compilation similar to webpack. Parcel requires zero configuration. Refer to the official [docs](https://parceljs.org/getting_started.html) to get started.

### Using TypeScript

Jest supports TypeScript, via Babel. First, make sure you followed the instructions on [using Babel](#using-babel) above. Next, install the `@babel/preset-typescript` via `yarn`:

```bash
yarn add --dev @babel/preset-typescript
```

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

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

However, there are some [caveats](https://babeljs.io/docs/en/babel-plugin-transform-typescript#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](https://github.com/kulshekhar/ts-jest) instead, or just run the TypeScript compiler [tsc](https://www.typescriptlang.org/docs/handbook/compiler-options.html) separately (or as part of your build process).

You may also want to install the [`@types/jest`](https://www.npmjs.com/package/@types/jest) module for the version of Jest you're using. This will help provide full typing when writing your tests with TypeScript.

> For `@types/*` modules it's recommended to try to match the version of the associated module. For example, if you are using `26.4.0` of `jest` then using `26.4.x` of `@types/jest` is ideal. In general, try to match the major (`26`) and minor (`4`) version as closely as possible.

```bash
yarn add --dev @types/jest
```
