
#### Table of Contents

1. Introduction
2. Install Packages
3. Create babel.config.js
4. Create jest.config.ts
5. Change the Code sample.js to TypeScript sample.ts
6. Change the Jest sample.test.js to TypeScript sample.test.ts
7. Run npm run test

### Introduction

This blog shows how to get start use TypeScript to write code and also write in Jest.

### Install Packages

If you have not use Jest, can reference this to get start with Jest with JavaScript, [Get Start with Jest](/blog/post/start-setup-jest).

At here, we'll start install necessary NPM packages for use TypeScript at Jest and the code.

```
npm install --save-dev @babel/core @babel/preset-env @babel/preset-typescript @jest/globals @types/jest babel-jest ts-jest ts-node typescript
```

### Create `babel.config.js`

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

### Create `jest.config.ts`

```JavaScript
export default {
    clearMocks: true,
    collectCoverage: true,
    coverageDirectory: "coverage"
}
```

### Change the Code `sample.js` to TypeScript `sample.ts`

### Change the Jest `sample.test.js` to TypeScript `sample.test.ts`

```JavaScript
import {exponent, subtraction, sum} from '../src/sample';
import {describe, expect, test} from '@jest/globals';

describe('calculator', () => {
    test('test sum', () => {
        expect(sum(1, 2)).toBe(3);
    });

    test('test subtraction', () => {
        expect(subtraction(10, 2)).toBe(8);
    });

    test('test exponent', () => {
        expect(exponent(5, 2)).toBe(25);
    });
})
```

### Run `npm run test`

Now, if run `npm run test` and if everything works, should see test all passed and 100% coverage.


This blog shows how to get start use TypeScript to write code and also write in Jest.

How to use TypeScript with Jest


## Table of Contents

- [Introduction](#introduction)
- [Init NPM Repo and Setup Packages](#init-npm-repo-and-setup-packages)
- [Add Test Script in package.json](#add-test-script-in-packagejson)
- [Add JavaScript and Test](#add-javascript-and-test)
- [Run the Test](#run-the-test)
- [Conclusion](#conclusion)

## Introduction

This blog shows how to quickly get started testing JavaScript with Jest.

## Init NPM Repo and Setup Packages

Here we will set up the npm repo, then install the dependency package `jest`.

```
npm init -y
```

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

## Add Test Script in package.json

Add the `test` command with `jest`. Now if we run `npm run test`, it should run Jest with the default settings.

```Javascript
  "scripts": {
    "test": "jest"
  },
```

## Add JavaScript and Test

Here, create a file and add a few JavaScript functions.

```JavaScript
function sum(a, b) {
    return a + b;
}

function exponent(a,b) {
    return a ** b;
}

function subtraction(a, b) {
    return a -b;
}
module.exports = {
    sum,
    subtraction,
    exponent
};
```

Next, create a test file and add test code.

```JavaScript
const {exponent, subtraction, sum} = require('../src/sample');

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

test('test subtraction', () => {
    expect(subtraction(10, 2)).toBe(8);
});

test('test exponent', () => {
    expect(exponent(5, 2)).toBe(25);
});
```

## Run the Test

That's it! Now we can see the tests passed.

![Cloud Functions to Firestore](/images/start-setup-jest/img1.png)

## Conclusion

Setting up Jest for JavaScript testing is quick and simple. Initialize an npm project, install Jest as a dev dependency, add a test script, and write your test files. Jest handles the rest with its default configuration.


This blog shows how to quickly get started testing JavaScript with Jest.

Jest

How to use TypeScript with Jest

How to Get Started with Jest