paulirish / performance.now()-polyfill.js

Last active February 05, 2015


    
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            // @license http://opensource.org/licenses/MIT
// copyright Paul Irish 2015
 
 
// Date.now() is supported everywhere except IE8. For IE8 we use the Date.now polyfill
//   github.com/Financial-Times/polyfill-service/blob/master/polyfills/Date.now/polyfill.js
// as Safari 6 doesn't have support for NavigationTiming, we use a Date.now() timestamp for relative values
 
// if you want values similar to what you'd get with real perf.now, place this towards the head of the page
// but in reality, you're just getting the delta between now() calls, so it's not terribly important where it's placed
 
 
(function(){
 
  if ("performance" in window == false) {
      window.performance = {};
  }
  
  Date.now = (Date.now || function () {  // thanks IE8
	  return new Date().getTime();
  });
 
  if ("now" in window.performance == false){
    
    var nowOffset = Date.now();
    
    if (performance.timing && performance.timing.navigationStart){
      nowOffset = performance.timing.navigationStart
    }
 
    window.performance.now = function now(){
      return Date.now() - nowOffset;
    }
  }
 
})();