JQuery $(...).ready is not a function

This one happened to me many times. It usually means that some script override the $ variable, and after JQuery has been initialized. In other words there is a huge chance that one of a javascript libraries that you added recently overrides $. The best way to check if it's the case is to fire up following script under firebug script console.

alert($)

If the result is simmilar to this:

function (a,b){return new e.fn.init(a,b,h)}

Everything is ok, this is how $ looks when JQuery is in charge of it. But often I see something else. For example a code below means that mootools is also used and it takes over $ function:

function (B, C) { if (B && B.$family && B.uid) { return B; } var A = $type(B); return ($[A]) ? $[A](B, C, this.document) : null; }

And it means that some code did something nasty with $ variable. The next thing that I do is to read libraries, disable them, and follow a typical tracing path.