Vincent Hellot over at FuzzyCom teaches how to use dtrace to trace javascript problems on a Mac (using a specially compiled Firefox binary for OSX). He hints at being able to do it with Ruby on Rails as well. Haven’t tried this, but can’t wait to do so.
This post aims at introducing the DTrace debugging tool in the scope of a javascript application. It won’t get too deep in the wide field of DTrace functions but I hope it will give you an overview of how DTrace can help to solve performance and debugging issues in your javascript applications
[From FuzzyCom :: Using DTrace for javascript debug on OS X in firefox]