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AngularJS: Hot-Module-Replacement with babel-plugin

ofhouse profile image Felix Haus ・3 min read

Note:
In 2020 AngularJS will turn 10 years old and with it's final sunset is only 1.5 years away (on June 30, 2021) you should not start to write new applications using AngularJS!

Despite its age there are still some AngularJS applications out there.
While the most websites on the internet already have replaced AngularJS by something newer, there are still some pretty large AngularJS applications alive behind the safe firewalls of company-intranets.
So if you still have to deal with AngularJS there is some good news: While upgrading from AngularJS may not be an option for you, you can still give your development experience a decent upgrade by enabling hot-module-replacement on your project.

Upgrade your developer experience by using Hot-Module-Replacement

The only requirement for this is that your project is already uses a bundler (like webpack or Parcel) which supports hot-module-replacement (HMR) and babel to transform your source.

Next install the babel-plugin-ng-hot-reload package from npm:

npm i -D babel-plugin-ng-hot-reload     # npm or
yarn add -D babel-plugin-ng-hot-reload  # yarn

Now, update your .babelrc.js file and add the newly installed plugin:

// .babelrc.js
module.exports = {
  presets: [
    [
      '@babel/preset-env',
      {
        modules: false, // <- The plugin works with es-modules!
      },
    ],
  ],
  plugins: [
    'babel-plugin-ng-hot-reload',
  ],
};

When you are using Parcel no other configuration is necessary.
If you're using webpack, make sure to enable hot-module-replacement in your webpack.config.js:

// webpack.config.js
const webpack = require('webpack');

module.exports = {
  mode: 'development,
  entry: [
    `${require.resolve('webpack-dev-server/client')}?/`, // <- add
    require.resolve('webpack/hot/only-dev-server'), // <- add
    './src/index.js'
  ],
  output: {
    path: 'dist',
    filename: 'app.js',
    publicPath: '/',
  },
  module: {
    rules: [
      {
        test: /\.js$/,
        loader: ['babel-loader'],
        exclude: /node_modules/,
      },
      ...
    ],
  },
  resolve: {
    extensions: ['.js'],
  },
  plugins: [
    ...
    new webpack.HotModuleReplacementPlugin(), // <- add
  ],
  devServer: {
    hot: true, // <- add
  },
};

Now you can edit your HTML, CSS or JavaScript files and they should be replaced without a reload of your application.

Fore some more advanced use-cases here are some examples available on CodeSandbox:

Some words about babel-plugin-ng-hot-reload

Under the hood the plugin relies on the solid work of the ng-hot-reload library by Oskari Noppa.
Since this library originally provides a webpack-loader the usage was limited to webpack.
Another limitation from the loader is that it is only compatible with commonJS modules created by babel, so if your are using import and export syntax it gets rewritten to require('...') and module.exports = {...} which is incompatible with tree-shaking.

This babel-plugin takes a deeper look at your code by preserving the imports and exports and only adds the code required for the hot-reload to the modules which are interacting with angular.
So the code for the browser is less bloated and can use the same tree-shaking like the production version (Lazy-loaded AngularJS modules are also supported by the plugin).

If you want to know more, the the plugin and the examples are open source and available here:

GitHub logo ofhouse / babel-plugin-ng-hot-reload

Hot reloading for AngularJS apps via babel plugin.

🔥 babel-plugin-ng-hot-reload Build status

A babel plugin which enables hot module replacement in AngularJS applications.
The plugin is based on the ng-hot-reload webpack loader but is rewritten as babel plugin so that it is compatible with es-module syntax and every bundler which supports the hot-replacement API (e.g. webpack or parcel).

Getting started

To see it in action you can simply checkout the examples on CodeSandbox:

npm i -D babel-plugin-ng-hot-reload     # npm or
yarn add -D babel-plugin-ng-hot-reload  # yarn

Add the following to your babelrc.js file:

// without options
module.exports = {
  plugins: ['babel-plugin-ng-hot-reload'],
};
// with options
module.exports = {
  plugins: [
    [
      'babel-plugin-ng-hot-reload',
      {
        angularGlobal: false,
        forceRefresh: true

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