http://www.my-debugbar.com/wiki/CompanionJS/HomePage

Companion.JS (pronounced Companion dot JS or CJS) is a Javascript debugger for IE. The current version is 0.4.2.
Companion.JS adds the following features to IE :

• Detailled javascript error reporting (call stack and real file name where the error occured).
• "Firebug"-like Console API feature.
• Javascript console feature useful to inspect javascript objects at runtime.
• A toolbar icon to open the Companion.JS panel.