jquery.jsonp addresses issues with beforeSend and timeout

On the coat-tails of my previous post, I've come across the Google Code jquery-jsonp library and it's a saviour if you're working JSONP requests. Remember a JSONP request dynamically inserts a script tag into the DOM and doesn't use the same XMLHttpRequest as your typical AJAX request.

I ended up here because—much like beforeSend—the timeout parameter wasn't having any effect on my jsonp request: the request simply wouldn't time out despite the value supplied to this parameter.

In addition to supporting both beforeSend and timeout properties, jquery-jsonp adds some really nice caching support—both typical HTTP (aka "browser") caching and page-based caching that leverages the JavaScript VM's memory (apparently). Anyway it seems to work as advertised. Perhaps most importantly, the name of the callback can be changed.

A minified version of the code is available from Google Code and the documentation is concise and well-written with examples. 

.ajax beforeSend Doesn't Fire

I absolutely adore jQuery but there are some things that are just plain hard to do with the current version. One of those is cross-domain (JSONP) requests. No only is the setup convoluted but the requirements are exacting to arrive at a working solution for something that should be (?) reasonably simple. But I'll save the details for another time—for now, just know I'm building with jQuery and using JSONP to issue cross-domain requests.

Under the covers, that cross domain request is actually being issued by dynamically loading a new script tag in the DOM, even though everything's still handled through the $.ajax() function. It's workable, of course, but since there are no XMLHTTPRequests involved, the behaviour is apparently somewhat different. In my particular case, I was wiring up  'beforeSend and 'complete' event handlers to show and hide a spinner across the lifetime of the request; the 'complete' handler was firing fine but the 'beforeSend' handler wasn't firing at all.

A response by SLaks to a Stack Overflow post reminded me the request mechanism with JSONP is different and implied 'beforeSend' wouldn't work with this setup. His response instead suggested showing the spinner after the $.ajax call and this did the trick for me.