Best Way To Loop Through Javascript Array Of Objects

var person = {firstName:"Adam", lastName:"Hassan"};
var keys = [];
for(var k in person){
keys.push(k);
document.write(person[k]);
document.write("<BR>");
}
document.write("total " + keys.length + " keys: " + keys);

var person = { first: "Adam", last: "Hassan" };
Object.keys(person).forEach(function(key) {
document.write(key, person[key]);
});

<script>
var person = {firstName:"Adam", lastName:"Hassan"};
var keys = [];
for(var key in person){
//use array to store properties of an object

keys.push(key);
//also you can make sure that the key you get is an actual property of an object

if (person.hasOwnProperty(key)) {
document.write(key + " -> " + person[key]);
document.write("<BR>");
}
}
document.write("total " + keys.length + " keys: " + keys);
</script>