test-object-loop.js

var object = {}, i = 0;

while (i++ < 100000) {
	object['user' + i] = i;
}

// fastest
console.time('keys for');
var result;
var keys = Object.keys(object);
	for (var i = 0, l = keys.length; i < l; i++) {
		result = object[keys[i]];
	}
console.timeEnd('keys for');

console.time('keys forEach');
var result, keys = Object.keys(object);
keys.forEach(function(key){
	result = object[key];
});
console.timeEnd('keys forEach');

// slowest
console.time('in hasOwnProperty');
var key, result;
for(key in object) {
	if (object.hasOwnProperty(key)) {
		result = object[key];
    }
}
console.timeEnd('in hasOwnProperty');

console.time('in');
var key, result;
for(key in object) {
	result = object[key];
}
console.timeEnd('in');