All too often front-end JavaScript code has been considered a second class citizen, and when treated without due care and attention it can be buggy and hard to maintain. This attitude is changing though, and thanks to the rapid growth in popularity of JavaScript as a first-class language, there is a large and expanding ecosystem of tools that a developer should know to make their client-side code as “clean” as the rest of their stack. This talk aims to introduce and discuss how to implement modularisation, functional idioms and testing in JavaScript in an idiomatic way, to allow you to code JavaScript to a higher quality and, ultimately, more sustainably.