Why do some sites use jquery with a $j instead of just a $?

Question

I generally use this in jquery

$(document).ready(function() {
    //stuff
}

I was just on a site that heavily uses jquery and they call it using

$j(document).ready(function() {
    //stuff
}

On this site they start almost everything out with a j...

function PostComment(form) {
  form = $j(form);
  $j('#CommentSubmitButton').hide();
  $j('#CommentInProgress').show();
  $j.post('/utils/ajaxhandler.aspx', form.serialize(), function(data) {
    $j('#CommentInProgress').hide();
    $j('#CommentSubmitButton').show();
  });
}

Is this just another way of doing it or is this dependent on a differnt version of jquery or other?

Answer 1

You can define, how you want to call the jquery functionality. Maybe this site uses another library, which reserves the $, and for that reason used the alias $j.

Answer 2

This is to avoid colision with other libraries with:

 jQuery.noConflict();

For instance some libraries like prototype also use the $ sign, and if you end up using both it will most likely break. If you developed your jquery functions using $j it won't.