Make Your Webpack Bundles Clean and Lean

A team from Codurance (including myself) are currently helping out a client on a Javascript Brownfield project. It’s a news application with a worldwide customer base and has a stack that includes ReactJS, Express, Webpack, and a host of other libraries.
Recently a member of the team noticed that certain parts of the application were serving up bundles of nearly 2mb! I was quite new to Webpack at the time and jumped at the opportunity to get to know Webpack better and see if I could try and solve the problem.