My contribution for Project 3 runs primarily on JavaScript. JavaScript seems to be a very useful system, but it has its own language and seems to be more complex than CSS. I wouldn’t say I’ve mastered it by any definition.
The most useful tools I’ve found for learning basic JavaScript have been:
W3Wschools (http://www.w3schools.com/js/ )
And Code Academy (https://www.codecademy.com/learn/javascript)