Node Hot Loader

Node Hot Loader is a small tool for Hot Module Replacement support for Node.js application development with webpack. Under the hood it uses webpack and babel, so you can use all you need configurations in config files for babel and webpack.

Node Hot Loader, by default, runs all webpack entries in the same single process or in forked process, if you set corresponding option.

The most suitable use case for Node Hot Loader is hot-reloaded express application. Express application can contains API and frontend together, moreover frontend can use own HMR, e.g. React with React Hot Loader. See how to setup React HMR with Express in React Hot Loader docs. Thus, both the frontend and the server will be hot-reloadable.

Node Hot Loader also supports webpack config files written on ES2015+/TypeScript (via babel). For using ES2015+/TypeScript in webpack configuration you have to provide babel configuration file in project root directory.

If you have suggestions or you find a bug, please, open an issue or make a PR.

Installation

npm install --save-dev node-hot-loader webpack
# or
yarn add --dev node-hot-loader webpack

Command line usage

Node Hot Loader uses yargs for parsing command line arguments.

Usage: node-hot {options}

Options

Name	Description	Note
--config	Path to the webpack config file.	If not set then search webpack.config.js in root directory.
--fork	Launch compiled assets in forked process with optional node exec arguments.
--args	List of arguments for forked process.
--autoRestart	Auto restart forked process if unaccepted modules discovered.
--inMemory	Launch compiled assets in memory fs. Not worked with forked process.
--logLevel	Log level related to webpack stats configuration presets names.	If not set then uses webpack stats configuration.

Usage example

node-hot --config webpack.config.server.js
# or
node-hot --logLevel minimal
# or
node-hot --fork
# or
node-hot --fork --autoRestart
# or
node-hot --fork=--arg1,--arg2 --
# or
node-hot --fork --args=--arg1,--arg2
# or just
node-hot
# Use the --help option to get the list of available options

Of course, you can add script into you package.json:

"scripts": {
  "start": "node-hot --config webpack.config.server.js"
}

and then run with your favorite package manager:

npm run start
# or
yarn run start

Webpack plugin

import NodeHotLoaderWebpackPlugin from 'node-hot-loader/NodeHotLoaderWebpackPlugin';

// Webpack configuration
export default {
  plugins: [
    // All options are optional
    new NodeHotLoaderWebpackPlugin({
      force, // boolean. true - always launch entries, false (by default) - launch entries only in watch mode.
      fork, // boolean | string[]. For example ['--key', 'key value'].
      args, // string[]. For example ['--arg1', 'arg2'].
      autoRestart, // boolean
      logLevel, // string
    }),
  ],
};

and run webpack in watch mode:

webpack --watch

The minimum required configuration:

Node Hot Loader adds all necessaries to webpack config if not present already (e.g. HotModuleReplacementPlugin), but it's require the minimum configuration in your webpack config file:

export default {
  output: {
    // Webpack can't find hot-update if output file is not directly in output.path.
    // For example, filename: 'js/[name].js' will not work.
    // However, I have no many tests for that.
    filename: '[name].js',
  },
};

Express Hot Reload Example

import app from './app'; // configuring express app, e.g. routes and logic

function startServer() {
  return new Promise((resolve, reject) => {
    const httpServer = app.listen(app.get('port'));

    httpServer.once('error', (err: any) => {
      if (err.code === 'EADDRINUSE') {
        reject(err);
      }
    });

    httpServer.once('listening', () => resolve(httpServer));
  }).then((httpServer) => {
    const { port } = httpServer.address();
    console.info(`==> 🌎 Listening on ${port}. Open up http://localhost:${port}/ in your browser.`);

    // Hot Module Replacement API
    if (module.hot) {
      let currentApp = app;
      module.hot.accept('./app', () => {
        httpServer.removeListener('request', currentApp);
        import('./app')
          .then(({ default: nextApp }) => {
            currentApp = nextApp;
            httpServer.on('request', currentApp);
            console.log('HttpServer reloaded!');
          })
          .catch((err) => console.error(err));
      });

      // For reload main module (self). It will be restart http-server.
      module.hot.accept((err) => console.error(err));
      module.hot.dispose(() => {
        console.log('Disposing entry module...');
        httpServer.close();
      });
    }
  });
}

console.log('Starting http server...');
startServer().catch((err) => {
  console.error('Error in server start script.', err);
});

Troubleshooting

Running Node Hot Loader inside a Docker container

If you attempt to run the Node Hot Loader inside a Docker container, it will start and serve as expected, but will not Hot Module Reload without some additional configuration. Add the following to your webpack config:

module.exports = {
  //...
  watchOptions: {
    poll: 1000, // Check for changes every second
  },
};

This instructs webpack to poll for changes (every second) instead of watching. This is necessary because watching does not work with NFS and machines in VirtualBox. See Webpack Configuration docs for more information.

Debugging in an IDE

If you have problems with sourcemaps or breakpoints, try to launch node-hot-loader with fork option. Also you may have to use one of the eval sourcemap styles for the devtool option in the webpack config.

License

MIT