There's an existing .ts definition in DefinitelyTyped.

And Zepto, of course. It's also AMD-capable. Bacon.js includes a "sink" mechanism to build custom event streams to fit any need.

Makes it easy to integrate to any application or framework.

Lower-level constructs map better to higher-abstraction functional languages (e.g., Haskell), but for practical JavaScript programming, a higher-level set of operations maps more naturally to chained methods and it's less verbose and much easier to learn.