JQuery Works On My Page, But Firebug Says $ Is Not Defined Error. Why And How To Avoid It?

UPDATE: Finally I found the solution, it was totally my fake. There were an iframe tag on the site, and in the external file I didn't include jQuery. But I learned a lot from your

Solution 1:

Try changing all $ characters with "jQuery". They are possibly conflicting with an other library you are including.

as in;

$(document).ready(function() {} );

to

jQuery(document).ready(function() {} );

Solution 2:

Based on the error, the problem is in the 3rd script. Try moving the second script below the 3rd one. The advexpad maybe overwriting the $ shortcut in their module. Also including jquery first isn't recommended, but rather required in your case. Since the 3rd script uses it, you have to have it precede it.