I'm one of the creators of Sourcegraph, which does have results for many JavaScript frameworks. You can find examples from all across GitHub, and you can search by function name or full-text documentation.

JS is hard to analyze, but we're working hard on getting better--and the analysis code is open source[1].

https://sourcegraph.com/github.com/joyent/node

https://sourcegraph.com/github.com/jashkenas/underscore

https://sourcegraph.com/github.com/caolan/async

[1] https://sourcegraph.com/github.com/sourcegraph/jsg