webpack.config.js

 var path = require('path');
 var webpack = require('webpack');
const TerserPlugin = require("terser-webpack-plugin");

 var PROD = (process.env.NODE_ENV === 'production');

 module.exports = {
     entry: './controller.js',
     mode: PROD ? 'production' : 'development',
     output: {
         path: path.resolve(__dirname),
         filename: 'meteorogram.js'
     },
     module: {
         rules: [
             {
                 test: /\.js$/,
                 use: [
                     {
                        loader: 'babel-loader',
                        options: {
                            presets: ['@babel/preset-env'],
                        }
                     }
                 ]
             }
         ]
     },
     externals: {
         Plotly: 'Plotly'
     },
     stats: {
         colors: true
     },
     devtool: 'source-map',
     optimization: {
         minimizer: [new TerserPlugin()],
         minimize: true,
     }
 };