A few Cesium devs, including me, have been working on a new book, WebGL Insights.
Matt Amato and Kevin Ring contributed a chapter, Getting Serious with JavaScript, that covers how we do large-scale JavaScript development in Cesium, including modularity, performance, and testing. This chapter is free online:
http://webglinsights.github.io/downloads/WebGL-Insights-Chapter-4.pdf
This is a worthwhile read for all Cesium users and contributors.
Patrick