var foo = [];
var i, start, end, length = 10000000;
for (i = 0; i < length; i++) {
 foo.push(i);
};


start = (new Date()).getTime();
for (i = 0; i < length; i++) {
}
end = (new Date()).getTime();

console.log(" FOR LOOP " + (end-start));

start = (new Date()).getTime();
for (i in foo) {
}
end = (new Date()).getTime();


console.log(" FOR VAR IN " + (end-start));