JavaScriptCore is a framework for Mac OS X that takes the cross-platform KJS library (part of the KDE project), combines it with the PCRE regular expression library, and makes it work with Mac OS X technologies.

The current version of JavaScriptCore is based on the KJS library from KDE 3.0.2. The few changes that are specific to JavaScriptCore are marked with #if APPLE_CHANGES. Other changes to improve performance and web page compatibility are intended for integration into future versions of the KJS library.

–http://developer.apple.com/darwin/projects/webcore/