Benchmarks of various JS reverse loop implementations

gistfile1.js

var arr = []

for (var i = 0; i < 100000; i++) {
	arr.push(i+1);
}

// This is what the coffeescript compiler produces for 'sum += arr[x] for x in [arr.nexts.length - 1..0]'
var coffee = function() {
	var x, _ref, sum = 0;
	for (x = _ref = arr.length - 1; _ref <= 0 ? x <= 0 : x >= 0; _ref <= 0 ? x++ : x--) {
	  sum += arr[x];
	}

	return sum;
}

var js = function() {
	var sum = 0;

	for (var x = arr.length - 1; x >= 0; x--) {
		sum += arr[x];
	}

	return sum;
}

var sam = function() {
	var sum = 0;

	var x = arr.length;
	while (x--) {
		sum += arr[x];
	}

	return sum;
}

var time = function(f) {
	var start = Date.now();
	for (var i = 0; i < 100; i++) {
		f();
	}
	var end = Date.now();

	return end - start;
}

console.log("coffee: " + time(coffee));
console.log("js: " + time(js));
console.log("sam: " + time(sam));