var now = (function() {
// Returns the number of milliseconds elapsed since either the browser navigationStart event or
// the UNIX epoch, depending on availability.
// Where the browser supports 'performance' we use that as it is more accurate (microsoeconds
// will be returned in the fractional part) and more reliable as it does not rely on the system time.
// Where 'performance' is not available, we will fall back to Date().getTime().
var performance = window.performance || {};
performance.now = (function() {
return performance.now ||
performance.webkitNow ||
performance.msNow ||
performance.oNow ||
performance.mozNow ||
function() { return new Date().getTime(); };
})();
return performance.now();
});