Cypress preprocessor for bundling JavaScript via webpack

Usage no npm install needed!

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Cypress Webpack Preprocessor

Cypress preprocessor for bundling JavaScript via webpack


npm install --save-dev @cypress/webpack-preprocessor

This package relies on the following peer dependencies:

  • @babel/core
  • @babel/preset-env
  • babel-loader
  • webpack

It is likely you already have these installed either directly or as a transient dependency, but if not, you will need to install them.

npm install --save-dev @babel/core @babel/preset-env babel-loader webpack


This version is only compatible with webpack 4.x+ and Babel 7.x+.

  • If you need webpack 2 or 3 support, use @cypress/webpack-preprocessor 1.x
  • If you need Babel 6 support, use @cypress/webpack-preprocessor <= 2.x

By default, this plugin (and all Cypress plugins) run in the Node version that is bundled with Cypress. Alternatively, you can use the Node found on your system by setting nodeVersion: system configuration option. A common use case for using the system Node are native dependencies like node-sass.


In your project's plugins file:

const webpackPreprocessor = require('@cypress/webpack-preprocessor')

module.exports = (on) => {
  on('file:preprocessor', webpackPreprocessor())



Pass in options as the second argument to webpack:

const webpackPreprocessor = require('@cypress/webpack-preprocessor')

module.exports = (on) => {
  const options = {
    // send in the options from your webpack.config.js, so it works the same
    // as your app's code
    webpackOptions: require('../../webpack.config'),
    watchOptions: {},

  on('file:preprocessor', webpackPreprocessor(options))


Object of webpack options. Just require in the options from your webpack.config.js to use the same options as your app.


  mode: 'development',
  module: {
    rules: [
        test: /\.jsx?$/,
        exclude: [/node_modules/],
        use: [{
          loader: 'babel-loader',
          options: {
            presets: ['@babel/preset-env'],

Source maps are always enabled unless explicitly disabled by specifying devtool: false.

Webpack mode is set to development if not present. You can set mode to "development", "production" or "none".

use babelrc

If you have a .babelrc file and would like to use it, then you must delete options.presets from the default Webpack options

const webpackPreprocessor = require('@cypress/webpack-preprocessor')
const defaults = webpackPreprocessor.defaultOptions
module.exports = (on) => {
  delete defaults.webpackOptions.module.rules[0].use[0].options.presets
  on('file:preprocessor', webpackPreprocessor(defaults))


Object of options for watching. See webpack's docs.

Default: {}


An array of file path strings for additional entries to be included in the bundle.

By necessity, this preprocessor sets the entry point for webpack as the spec file or support file. The additionalEntries option allows you to specify more entry points in order to utilize webpack's multi-main entry. This allows runtime dependency resolution.

Default: []


const webpackPreprocessor = require('@cypress/webpack-preprocessor')

module.exports = (on) => {
  const options = {
    webpackOptions: require('../../webpack.config'),
    additionalEntries: ['./app/some-module.js'],

  on('file:preprocessor', webpackPreprocessor(options))

Modifying default options

The default options are provided as webpack.defaultOptions so they can be more easily modified.

If, for example, you want to update the options for the babel-loader to add the stage-3 preset, you could do the following:

const webpackPreprocessor = require('@cypress/webpack-preprocessor')

module.exports = (on) => {
  const options = webpackPreprocessor.defaultOptions

  on('file:preprocessor', webpackPreprocessor(options))


You can see debug messages from this module by running with environment variable


You can see Webpack bundle diagnostic output (timings, chunks, sizes) by running with environment variable


Webpack stats


Use the version of Node that matches Cypress.

Build the typescript files:

yarn build

Watch the typescript files and rebuild on file change:

yarn build --watch

Run all tests once:

npm test

Run tests in watch mode:

npm run test-watch


This project is licensed under the terms of the MIT license.