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Integrating Webpack and Babel in a legacy project

Let's say you have an old legacy application written in PHP or Perl that is used a lot over time. And while developing you come across a new fancy javscript library with instructions like npm i super-dope-library and a code example like import {coolStuff} from 'super-dope-library'. How is that going to work?

What do you need#

  • Package manager - Yarn or NPM. This let's you install and manage third party packages.
  • Module bundler - For example webpack or esbuild. Combines all the javascript from your project and the third party packages in optimized files.
  • Transpiler - For example Babel. Compiles new JavaScript code to old JavaScript code so older browsers understand it.

The examples in this post use NPM, webpack and Babel. The alternatives are all sharing the same concepts

Setup NPM, webpack and Babel#

Node and NPM need to be installed and accessible from the commandline. Then run npm init at your project root. This will create a package.json file.

After that install the webpack and Babel dependencies:

npm install -D babel-loader @babel/core @babel/preset-env webpack webpack-cli

This will add dependencies to the package.json file. Now add a webpack.config.js file to the root of the project:

const path = require('path');
module.exports = {
entry: './src/index.js',
output: {
path: path.resolve(__dirname, 'dist'),
filename: 'bundle.js',
module: {
rules: [
test: /\.m?js$/,
exclude: /(node_modules|bower_components)/,
use: {
loader: 'babel-loader',
options: {
presets: ['@babel/preset-env']

The entry file ./src/index.js will be the starting point of the Javascript and can be changed to a location that fits the current project.

The bundled and transpiled output file will be stored in <project-root>/dist/bundle.js. This can also be a location that fits the current project.

Writing code that uses a NPM package#

The pluralize NPM package can be used to pluralize words. Let's create a high-end application where a user can enter a random english word and see the pluralized version:

Install the library:

npm install pluralize

Add the following code to ./src/index.js:

import pluralize from 'pluralize'
const word = prompt("Enter an English word to pluralize", "cow");
const pluralized = pluralize(word);

Create the /dist/bundle.js file:


Integrate it in a legacy project#

After the bundle.js file is created it is fairly simple to integrate it. Just add the following script tag somewhere in the HTML and make sure the file is served by the webserver.

<script src="/dist/bundle.js" />

Github Example#

The steps above are implemented in an example PHP project: https://github.com/jurruh/legacy-php-webpack-babel-example


  • It is not necessary to ship the node_modules folder and the untranspiled Javascript code to production. These can be removed in the build process to gain smaller packages.
  • Add the dist folder to .gitignore. The code can be generated and therefor it should not be in version control.
  • You should explore the webpack CLI to see what is capable of: https://www.npmjs.com/package/webpack-cli