It’s been a while since I actually encountered this particular nugget of advice1, but I thought I’d go ahead and make a quick post out of it anyway.
This is the kind of totally random and arbitrary development structure Wordpress has adopted that doesn’t really seem to ever be documented anywhere. If you don’t already know this kind of thing, you could very well be in store for major development and debugging headaches.
Anyway, here we go… If you’re using the built-in jQuery Javascript library that’s included in Wordpress since version 2.2, don’t use the handy-dandy $() function. In Wordpress, $() is reserved for the Prototype library, which is also bundled2.
Instead, for interoperability, be sure to use jQuery() instead, which should accomplish the same thing.
A bad example:
var username = $('#username').val();
If Prototype were to be loaded on the page this snippet of JS is running on, it would throw an error, since it uses a different pattern for selecting DOM elements.
A good example:
var username = jQuery('#username').val();
This line should work on any page, regardless of library conflicts. It’s a couple extra characters to type, but in the end it’s really for the best - you get portability, and it’s more self-explanatory which library is being used when you go back to look at this code in 6 months.
I’m planning another, similar, Javascript-related post as soon as I get a few more minutes to make it coherent. Stay tuned, and happy coding!