[someguy1233]

I'm surprised nobody has mentioned TypeScript. I've been using it in one of my projects recently (WebStorm even has a file watcher that works with very little set up on my Macbook).

TypeScript is pretty good at giving you a taste of ES6, it brings in a lot of features from ES6, such as the new classes, default arguments, generics, as well as a few of it's own features (interfaces, optional static type checking).

They ship it as a node module, so you can just "npm install -g typescript" and it's ready to go. As much as I dislike Microsoft, Typescript is something that seems to work well, and unlike Coffeescript, I can quite happily paste in standard Javascript code (even most ES6 code) and it won't break my source.