JavaScript loop performance

performance_test.js

var i = 500000, ar = [], startTime, duration, output = {};

while(i--) {
	ar.push(i);
}

// jQuery
startTime = new Date().getTime();
$.each(ar, function(index, item) {
	//
});
duration = new Date().getTime() - startTime;
output.jquery = duration;

// Underscore
startTime = new Date().getTime();
_.each(ar, function(item, index) {
	//
});
duration = new Date().getTime() - startTime;
output.undescore = duration;
//-----

// ECS5
startTime = new Date().getTime();
ar.forEach(function(item, index) {
	//
});
duration = new Date().getTime() - startTime;
output.foreach = duration;
//----

//For
startTime = new Date().getTime();
var len = ar.length;
for(i=0;i<len;i++) {
	//
}
duration = new Date().getTime() - startTime;
output.for_regular = duration;
//----

//For rev
startTime = new Date().getTime();
i = ar.length;
for(i = ar.length; i > 0; i--) {
	//
}
duration = new Date().getTime() - startTime;
output.for_reverse = duration;
//----

//While
startTime = new Date().getTime();
i = ar.length;
while(i--) {
	//
}
duration = new Date().getTime() - startTime;
output.while_reverse = duration;
//----


for(var key in output) {
	$('body').append('<p>' + key + ': ' + output[key].toString() + ' ms</p>');
}