As of OS X 10.9 and iOS 7, Apple supplies an official Objective-C API to their JavaScript interpreter, so you no longer need to have web views and pages and stuff to use it. Unfortunately, it's very poorly documented at this time. However, it's open source, and the source code contains comments that Apple's "headerdoc2html" tool can make sense of. So, I ran that on all the files in the JavaScriptCore APIs directory, pulled out all the "Classes" stuff, arranged some things, and threw it on this site.
JavaScriptCore