Its user interface allows the user to set breakpoints and/or step through execution of script code line by line, and examine values of variables and properties after any step.
In effect, it provides a way for developers to see script code behavior as it runs, thus eliminating much of the guess-work when things do not quite work as intended.
Also, Internet Explorer 8 comes with a different, tightly integrated JScript debugger part of the Internet Explorer Developer Tools.
[1] According to Microsoft, the Script Debugger provides these traditional debugging features:[2] Additionally, it can open and edit HTML pages, and it supports script colorization for improved readability.
[2] The debugger has several limitations, including the following:[3] After installation, new options can be found in Internet Explorer's Script Debugger menu, which gets added in the View menu.