Hi Rob,
Thanks for your work on jscript. Unfortunately fixing Valgrind on jscript is not going to be easy. Most of your fixes are good, except clear_global part and "jscript: Fix a circular reference caused by object and function objects being able to have properties that are objects and functions." patch. I've sent a test showing that Windows doesn't do that. To fix it properly we need to implement a garbage collector. I've designed it in the very early days of jscript, but I never had time to implement it.
Thanks, Jacek