React Router - What's Your Build Process?

Facebook's build process is a little more complex than you'd like. What are you using for the build at Facebook? I'm sure there are like multiple steps and multiple things involved, but what does it generally kind of look like? So for React itself, a lot of it is custom. We also do make use of roll up as our bundler and Google closure compiler to minify the code after it's bundled together. But we also have a lot of custom logic because certain things behave differently in certain environments.