With IE you can use Microsoft Script debugger and Visual Studio as debuggers.
You can download it form Microsoft website.
To use the debugger, first you have to enable script debugging. Go to tools- options- tab. Make sure that “Disable Script Debugging (other)” and “Disable Script Debugging (Internet Explorer) are NOT checked.
It will create a breakpoint automatically.
Select yes. Then it will display possible set of debuggers.
Now you are debugging. Just step into as you do in any 0ther debugger.
You can use command window to to execute codes. From this little window you can easily check and re-assign values (at "run-time") to any of the variables that have been defined. Launch it from the View menu of the debugger or by clicking the button on the very right-hand-side of the toolbar.