Date.now = function() {
    return new Date(); };

Date.now was introduced as a native method in ECMAScript 5.1 (ECMA-262)
This should be updated to use a fallback/polyfill or removed completely to avoid potentially breaking any features that rely on the output from the new standardised method.

I noticed this was interfering with some transition/animation logic in some other plugins I was using.

See https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Date/now or below for polyfill

if (!Date.now) {
  Date.now = function now() {
    return new Date().getTime();
  };
}