gistfile1.js

// Javascript Benchmark Declaring len inside and outside of a for loop
// Populate array with 0..100
var arr = []
for (var i=0; i<1e3; ++i) { arr[i] = i; }

// Declare len outside of the for
function outfor(a) {
	var len = a.length;
	for (var i=0; i<len; ++i);
}

// Declare len inside of the for
function infor(a) {
	for (var i=0, len=a.length; i<len; ++i);
}

// Run outfor 100000 times
(function() {
	console.time("outfor");
	for (var i=0; i<1e5; ++i) { outfor(arr); }
	console.timeEnd("outfor");
})();

// Run infor 100000 times
(function() {
	console.time("infor");
	for (var i=0; i<1e5; ++i) { infor(arr); }
	console.timeEnd("infor");
})();