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Greasemonkey Hacks by Mark Pilgrim

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Hack #46. Trace XMLHttpRequest Activity

Log XMLHttpRequest calls into JavaScript Console.

XMLHttpRequest is a JavaScript technique that enables a page to interact with the server without having to reload the entire page. This nonstandard API was first developed by Microsoft for Internet Explorer, but it was later picked up and implemented by most other browsers, including Firefox. Once used by only a few, it is now becoming more mainstream in the development of web applications.

The renewed interest for rich web applications such as Gmail, MSN Web-Messenger, and A9 Search, has crystallized a new nickname for the technique: AJAX.

Tip

Jesse James Garrett coined this term in early 2005 as a shorthand for "Asynchronous JavaScript And XML."

A large number of frameworks now make use of the XMLHttpRequest object, trying to abstract the API and make it easier to use for a larger portion of hackers. However, as with most abstractions, there are still many times when you need to look under the hood.

Traditional debugging tools allow you to do that. You can install HTTP sniffers such as the LiveHTTPHeaders extension; you can test code interactively with the Venkman JavaScript debugger or the JavaScript shell; you can just litter your code with JavaScript alert statements. But these tools often offer too much or too little of what you actually need. This user script approaches debugging from a different angle, by focusing on the XMLHttpRequest interactions themselves and providing lightweight ...

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