@adam_anything provided a good hint, but in my case, actually webpack@4.42.1, webpack optimization option is default true. In aspect of this episode, we should provide functionality which could switch on/off minimize options as environment variable set production or not.

Let's do this.

// webpack.config.js
        ]
    },
    optimization: {
        minimize: false,
    }
}

if (process.env.NODE_ENV === 'production') {
    module.exports.optimization.minimize = true;
}

then,

// package.json
 "scripts": {
    "dev": "node_modules/.bin/webpack",
    "production": "NODE_ENV=production webpack",
    "watch": "npm run dev -- --watch"
  },

I think that it's more appropriate. :)

Minification and Environments