Jest Preview ??

Preview your HTML code while using Jest

Jest Preview Demo

All Contributors

PRs Welcome npm

Why jest-preview

When writing tests using Jest, we usually debug by reading the HTML code. Sometimes the HTML is too complex and it’s hard to imagine how the UI looks in our head. jest-preview initiates a server and serve your HTML in a browser, then you can see your actual UI visually. This way, it helps you debug jest tests faster.

jest-preview is initially design to work with jest and react-testing-library. However it’s framework-agnostic and you can use it with any testing libraries.


  • ? Preview your actual app’s HTML in a browser.
  • ? Auto reload browser when execute preview(htmlContainer).
  • ? Support CSS:
  • ? Support viewing images.



  1. Install jest-preview

npm install jest-preview
# Or
yarn add jest-preview
pnpm install jest-preview
  1. Create cssTransform.js and fileTransform.js

// config/jest/cssTransform.js
'use strict';

const { processCss } = require('jest-preview');

module.exports = {
  process(src, filename) {
    return processCss(src, filename);

// config/jest/fileTransform.js
'use strict';

const { processFile } = require('jest-preview');

module.exports = {
  process(src, filename) {
    return processFile(src, filename);
  1. Configure jest’s transform to intercept CSS and files

// jest.config.js
transform: {
    "^.+\\.css$": "<rootDir>/config/jest/cssTransform.js",
    "^(?!.*\\.(js|jsx|mjs|cjs|ts|tsx|css|json)$)": "<rootDir>/config/jest/fileTransform.js",
  1. (Optional) Configure external CSS

Sometimes, there are some CSS files imported outside your current test components (e.g: CSS imported in src/index.js, src/main.tsx). In this case, you can manually add those CSS files to jest-preview by jestPreviewConfigure.

  // jest.config.js
    setupFilesAfterEnv: ["./config/jest/setupTests.js"],

// ./config/jest/setupTests.js
import { jestPreviewConfigure } from 'jest-preview';

  externalCss: [


  1. Update to package.json

  "scripts": {
    "jest-preview": "jest-preview"

Optionally, you can use npm-run-all to run jest and jest-preview server in parallel

  "scripts": {
    "test:debug": "npm-run-all -p test jest-preview"
  "devDependencies": {
    "npm-run-all": "latest"
  1. Run the jest-preview server

# You can use PORT to customize port, default to 3336
npm run jest-preview
# Or
yarn jest-preview
pnpm run jest-preview
  1. Preview your html from jest. Following code demo how to use it with react-testing-library

import preview from 'jest-preview';

describe('App', () => {
  it('should work as expected', () => {
    const { container } = render(<App />);'increase'));'increase'));

    // Open http://localhost:3336 to see the preview


Then visit http://localhost:3336 to see the preview

Preview your jest test in the browser

Upcoming features

  • Support css-in-js
    • ✅ Styled-components
  • Multiple preview
  • You name it

Run jest-preview locally

Install dependencies

npm install

To see the real demo app

npm run dev

Run jest and jest-preview simultaneously

npm run test

Open chrome at http://localhost:3336 to see the preview

Contributors ✨

Thanks goes to these wonderful people (emoji key):

Hung Viet Nguyen? ? ? Truong Nguyen? ? ?

This project follows the all-contributors specification. Contributions of any kind welcome!


This is open source software



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