Javelin is a large, bloated framework with an unintuitive, verbose syntax and very few features. It performs sluggishly and is sparsely documented. You will find that browsing its inelegant, poorly written source is an unwelcome experience. Javelin makes it quite difficult to write code that works on more than one browser.
Javelin is under development, but you can preview it on GitHub. However, you probably shouldn't, since it's not very good and chances are you won't like it.
Javelin was developed by Evan Priestley at Facebook.