Extends native 'performance' object with function that measure execution time

measure.js

(function(w){

  w.performance.measureTime = function(what, times){
    var results = [];
    for(var i=0; i<times; i++){
      var start = window.performance.webkitNow();
      what();
      var end = window.performance.webkitNow();
      results.push(end - start);
    }
    var sum = 0;
    for(var i in results){ sum += results[i] }
    
    return sum/results.length;    
  };
  
})(window)


// ======= Example of usage ==========

// executes console.log('dupa') 500 times and returns avarage execution time
performance.measureTime(function(){ 
  console.log('dupa') 
}, 500);