Recently I ran into an issue  while trying to use jQuery on a custom WordPress based Content Management System.  This particular system had a number of instances in which the framework was being referenced.  Normally you insert jQuery code using the dollar sign ($) like so:

$(document).ready(function() {
   $("a").click(function() {
     alert("Hello world!");
   });
 });

The problem arises when a different system grabs the $ variable.  All of the sudden you have multiple $ variables being used as objects from multiple libraries, resulting in the error console message “$ is not a function”.

Fortunately there is a pretty easy way of fixing this in the form of jQuery.noConflict.  Running this function gives control of the $ variable back to whichever library first implemented it.  This will help to ensure that jQuery won’t conflict with other instances of the $ object in other libraries.

But please note, in doing this, you are re-assigning the variable so you will only be able to access jQuery commands using the ‘jQuery’ variable (which has just replaced ‘$’).  So our above code example would look something like this:

jQuery.noConflict();
jQuery(document).ready(function() {
   jQuery("a").click(function() {
     alert("Hello world!");
   });
 });

It doesn’t seem to be a very common problem and only occurs when multiple instances of the object crop up, but that’s easy to do in WordPress when multiple plugins begin conflicting with each other.   Follow the link for the  full jQuery documentation on jQuery.noConflict