There are two projects you might be interested in:
- JavaScriptCore-iOS
- iMonkey
It is absolutely possible to build and ship a JavaScript engine with your iOS app, see http://www.phoboslab.org/log/2011/04/ios-and-javascript-for-real-this-time. Titanium does that, too: https://github.com/appcelerator/webkit_titanium/tree/master/Source/JavaScriptCore.
Also see http://www.phoboslab.org/log/2011/06/javascriptcore-project-files-for-ios.
I’ve also made a small app that shows how to use JSC on iOS: https://github.com/jfahrenkrug/AddressBookSpy
Enjoy.