There are so many benefits to using a modern JavaScript build system, but getting one to play nicely with a very old, very large codebase is not always easy. I’ll go over some of the more interesting problems we ran into at Etsy when migrating to Webpack from a system written in-house. We’ll talk about working in a large codebase without running out of memory, localizing our JavaScript into 15 languages without building it 15 times, and why 4 milliseconds kept us from launching the …