How can I find out which Javascript causes an Ajax request?

I'm having a problem with a Java JSF application: In a certain case, a user action causes an Ajax HTTP request that updates the UI correctly, but then i开发者_高级运维mmediately a second request is triggered, causing a second, incorrect update.

How can I find out (preferably using Firebug) where exactly that second request is triggered? There's a lot of minified framework JS code, so I don't know where to place breakpoints. Setting the form onsubmit handler to console.trace did not help, I suppose because these are independant Ajax requests.

While trying out the suggestions in the answers, I found that Firebug already has exactly what I need out of the box: the Console tab displays all requests, and for Ajax requests it shows the file and line number where they originate, which tells me where to set my breakpoint...

Using Firebug you can set Breakpoints on DOM (HTML) Mutation Events if you have some HTML changes in your UI update.

If the framework abstracts the AJAX requests, you should be able to trace the calls to the abstractions. For example, jQuery allows this through its global AJAX event handlers.

Another, more robust way to tackle the problem would be to replace the XHR object and trace calls made to it (i.e. if the framework does not provide the above abstraction or if the calls that you want to use don't use the abstraction). Just replace the GM_log with console.trace in the script at the end of the page and include it in the page you're testing.

What I personally have done in these case is using an HTTP proxy that can put a request or response 'on hold'. E.g. Burp Proxy ^{(this is actually a security tool, but it works great for debugging purposes)}

Start up the proxy and configure your browser to use it. Navigate to the page where the roque requests originates from and activate intercepting requests (this might take some practice as Burp Proxy can be a rather complicated tool).

Now do the user action, if all goes well the proxy intercepts it and waits for your confirmation to let it go through. Do this. Then you'll probably see the second request coming and being intercepted by the proxy as well. Don't let this one through, but instead switch to Firebug and suspend into the debugger. Hopefully you'll then be able to see where it originates from. Edit: on second thoughts, the asynchronous nature of AJAX probably means you won't be able to see what the exact spot is via this method anyway... :(

At least you can also configure it to intercept responses. Both requests and responses can be edited on the fly, which can be great for experimenting and debugging and might help in narrowing down the problem.

Might this would help, caller is a method in Function object of javascript.

console.log(arguments.callee.caller.toString());