measure.js

var REPEATS = 1000;


var _add = function (n1, n2) {
	return n1 + n2;
}
a = 4;
b = 5;
var alternatives = [
  {
    name: "No function call",
    action: function (){
      var c;
      for (var i = 0; i < 10000000; i++) {
        c = a + i;
      }
    }
  },
  {
    name: "Function call",
    action: function (){
      var c;
      var add = _add;
      for (var i = 0; i < 10000000; i++) {
        c = add(a,i);
      }
    }
  }
];

alternatives.forEach(function(alternative){
  var start = new Date();
  var repeat = REPEATS;
  for (var i=0; i< repeat;i++) {
    alternative.action();
  }
  var end = new Date();
  var totalMs = end.valueOf() - start.valueOf();
  var averageMs = totalMs/repeat;

  var result = alternative.name + " took " + averageMs + "ms - (" + repeat + " times, total time: " + totalMs + "ms)";
  if (typeof console !== "undefined") {
  	console.log(result);
  }
  if (typeof document !== "undefined"){
	document.body.innerHTML += result + "<br>";	
  }  
});