Firebug

Firebug provides a highly detailed profiling report. It will tell you how long each method invocation takes in a giant (detailed) table.

console.profile([title])
//also see
console.trace()

You need to call console.profileEnd () to end your profile block. See the console API here: http://getfirebug.com/wiki/index.php/Console_API

Blackbird

Blackbird also has a simpler profiler

• Blackbird official site from Wayback Machine
• Source from Google Code Archive
• Source from Github (pockata/blackbird-js: A fork of the cool Blackbird logging utility)
• Source from Github (louisje/blackbirdjs: Blackbird offers a dead-simple way to log messages)

Firebug+Firefox is a must have. And IE 8's developer toolbar also has a profiler built in (IE 8 ships with the developer toolbar).

Safari 4's web inspector also includes a profiler (although the version in the nightlies is improved wrt. recursive function calls). The Web Inspector also supports Firebug's profiler APIs.

Although Firebug has been mentioned, one additional thing you would want to look at with Firebug is a plugin for Firebug called FireUnit; John Resig talks about it in this blog post:

JavaScript Function Call Profiling

Hope that helps.

For JavaScript, XmlHttpRequest, DOM Access, Rendering Times and Network traffic for IE6, 7 & 8 you can use the FREEdynaTrace AJAX Edition

Chrome's Developer Tools has a built-in profiler.