Most compile-to-Javascript systems I've used have a "watch" mode which recompiles every time any source file changes. The initial build of a large project may t

Most compile-to-Javascript systems I've used have a "watch" mode which recompiles every time any source file changes. The initial build of a large project may take 30+ seconds, but after that, a rebuild when a source file changes takes a few seconds at most. And with some systems, you can even do live edits that apply immediately to running code, so you don't even have to refresh your browser, making development actually faster than not using any build process. (Good examples of this are hot module replacement for Browserify[1] and Webpack, and Figwheel for Clojurescript.) [1] https://github.com/AgentME/browserify-hmr/ https://github.com/AgentME/browserify-hmr/, a Browserify plugin made by me.