How to detect a JavaScript function with a certain signature has been registered?

Question

Say you have two functions with the following signatures:

1. addClass( class )
2. addClass( class, duration )

Answer 1

You can use the length property of the function object to check the signature. Example:

function x(a) {}
function y(a,b) {}

alert(x.length); // shows "1"
alert(y.length); // shows "2"