I had faced this issue in one of my development projects. I used jquery lavishly in every bit of my javascript code. Since during development, i used to write the scripts in the page itself, i didn’t have to bother much. But later when i decided to move the scripts to another external “.js” file, i found all my jquery methods failing. The common error being : $ not defined. After a lot of trial and errors, i was able to get to the bottom of the issue.
The solution:
You can have only one $.document(ready(){}); in the whole application. Remove all the DOM readiness checkers and add a single one in the main js file that you will be loading always.
The Relentless FrontEnd - Aackose Lal's Blog 
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You can have as many dom readiness checker as you want. Refer to http://docs.jquery.com/Tutorials:Multiple_$(document).ready() and http://stackoverflow.com/questions/1148241/jquery-is-it-bad-to-have-multiple-document-readyfunction
Checking for readiness can be done a lot of times, I agree. But the issue i faced was in having a readiness check in my external js and simultaneously as obstrusive javascript on the master page.
But then again at the end of the day, it gets rendered as multiple readiness checks, so may be the solution mentioned may not be accurate.
However in my case, it solved the problem. May be specific to .Net way.
Are you sure that was the problem. WordPress reserves $ for prototype, not jQuery. You need to use jQuery instead of $ or do the jQuery.noConflict thing
The noconflict is the solution to another problem, when it comes to integration of jquery with BlogEngine .Net or WordPress or any such systems with integrated scripting prototypes. Under such cases, you will have to use the noconflict. Check my post on jquery integration with BlogEngine
https://aackose.wordpress.com/2010/02/22/jquery-integration-with-blogengine-net/
But the problem i am describing here is that of jquery not working for external js files. Say in your project, you might have written jquery codes in the html or ASPX or PHP page. And now you want to move it to some external js file say ‘myscripts.js’. In that case, jquery breaks, even the site has $ being reserved. Problem is not with the use of $, but with the use of multiple $.document.ready() throughout your site.
Thanks a ton!.. I had the same issue..I was using multiple ” $.document.ready() ” in the code.. so jQuery wasn’t working..
I used a single $.document.ready() and my code is working fine!!..