The compiled code will be output to a dist directory in the project root. Between each build, we need to remove it so we are in a clean state. To do that in a cross-platform manner, we will use the rimraf package that can recursively delete files and folders.

1. Install the rimraf package to the dev dependencies:

      npm i -D rimraf

2. Add a build script for both the client and server bundles:

      "build:client": "cross-env NODE_ENV=production webpack --progress 
       --hide-modules --config webpack/client.js",
      "build:server": "cross-env NODE_ENV=production webpack --progress 
       --hide-modules --config webpack/server.js",

We set the NODE_ENV environment variable to 'production' and run the webpack command with the corresponding webpack configuration file.

3. Create a new build script that clears the dist folder and runs the two other build:client and build:server scripts:

      "build": "rimraf dist && npm run build:client && npm run 
        build:server",

4. Add a last script called start that runs the express server in production mode:

      "start": "cross-env NODE_ENV=production node server",

5. You can now run the build; use the usual npm run command:

      npm run build

The dist folder should now contain all the chunks generated by webpack, plus the server bundle and client manifest json files:

6. We can now start the express server:

      npm start