How to hunt down HTTP request?

Trying to optimize one web project.

It uses asp.net (webforms), bunch of jquery plugins and whatnot.

Problem: there's unnecessary HTTP request to localhost/undefined and that makes every request take ~1s longer than needed.

Question: is there any tactic to find guilty code?

Clue: undefined makes me think that there's JS involved.

Firebug log:

GET /undefined HTTP/1.1

Host: localhost:17817

User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; lv; rv:1.9.2) Gecko/20100115

Firefox/3.6

Accept: image/png,image/;q=0.8,/;q=0.5

Accept-Language: lv,en-us;q=0.7,en;q=0.3

Accept-Encoding: gzip,deflate

Accept-Charset: ISO-8859-13,utf-8;q=0.7,;q=0.7

Keep-Alive: 115

Connection: keep-alive

Referer: http://localhost:17817/Default.aspx

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if you right click a line in the code, it gives you a conditional breakpoint. Check the name of the variable that has the URL value, and set a condition when typeof URL === 'undefined' or url === 'undefined' and look at the stack

Just set breakproint at line 3400 (with no conditions). It does not go through there.

3397 ajax: function( s ) {

3398 // Extend the settings, but re-extend 's' so that it can be

3399 // checked again later (in the test suite, specifically)

3400 s = jQuery.extend(true, s, jQuery.extend(true, {}, jQuery.ajaxSettings, s));

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Narrowed issue down a bit => commented out 1 ascx controller that renders some images and uses gallerific jquery plugin and m开发者_开发技巧agic request dissapeared.

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Problem was with galleriffic plugin initialization. It couldn't find anchor and it's href for creating thumbnails when there were no images or something. It's cool now...

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Have you been able to identify what JS code is initiating the request? If you are using Firebug it should give you a line of code in the console window which is invoking the AJAX request. In the event it's something like a $.post() with a code line in the jQuery library, you can navigate the callstack within the Firebug plugin to try and figure out where the initial JS call is being invoked.

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You might want to try out the HTTP Watch.