gistfile1.js

var runs = 0;
function exec() {
    runs += this.y / 1337;
}

var x = {
    y: 1337,
    a: [1],
    go1: function() {
        for (var i = 0, al = this.a.length; i < al; ++i) {
            exec.apply(this);
        }
    },
    go2: function() {
        this.a.forEach(exec.bind(this));
    },
    go3: function() {
        for (var i = 0; i < this.a.length; ++i) {
            exec.apply(this);
        }
    },
}

d = Date.now();
for (var a = 0, l = 1024 * 1024; a < l; ++a) x.go1();
console.log('for', Date.now() - d);

d = Date.now();
for (g = 0, gl = 1024 * 1024; g < gl; ++g) x.go1();
console.log('for, global iterator', Date.now() - d);

d = Date.now();
for (var a = 0, l = 1024 * 1024; a < l; ++a) x.go3();
console.log('for, no length caching', Date.now() - d);

d = Date.now();
for (var a = 0, l = 1024 * 1024; a < l; ++a) x.go2();
console.log('foreach', Date.now() - d);

for 91
for, global iterator 106
foreach 481

for 89
for, global iterator 112
for, no length caching 90
foreach 526