JScript debugging is a critical part of Web development. With the intuitive, lightweight JScript debugger, the Developer Tools feature brings one-click simplicity to the end-to-end JScript debugging experience. After installing Internet Explorer 8, developers can debug JScript on any site loaded in Windows Internet Explorer.
To open Developer Tools within Internet Explorer 8, press F12; alternatively, on the Tools command bar, click the Developer Tools button.
Read the below link