In older browsers where Date.now() is unavailable, use [(new Date()).getTime()](<https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/getTime>) instead:

t = (new Date()).getTime();

Or, to provide a Date.now() function for use in older browsers, use this polyfill:

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