Microsoft Visual Studio AJAX Profiling Extensions is a new power tool to measure the performance of the portions of web applications that execute JavaScript inside the web browser.

From the website

Microsoft Visual Studio AJAX Profiling Extensions provides server-side extensions for profiling JavaScript code executed in a client browser. It does this by modifying the JavaScript as it leaves your server to capture timings when JavaScript functions are called and when they return. The data on function entry/exit timings is then transmitted back up to the server, from where it can be later downloaded and analyzed. This method of JavaScript profiling requires no modifications to the client and should work with most popular browsers. It has been tested with Internet Explorer and Firefox, and is likely to work with other browsers that support JavaScript, but your mileage may vary.

here is the link [via InfoWorld]