Webpack: Bundle.js – Uncaught ReferenceError: process is not defined

Update October 2020:

For webpack 5, you can reference process/browser from the appropriate plugins part of webpack.config.js

// webpack needs to be explicitly required
const webpack = require('webpack')

module.exports = {

/* ... rest of the config here ... */

  plugins: [
    // fix "process is not defined" error:
    // (do "npm install process" before running the build)
    new webpack.ProvidePlugin({
      process: 'process/browser',
    }),
  ]
}