Edit in JSFiddle

var result = document.getElementById('result');

function Ford() {
    this.company = "Ford Motor Company";
    this.found = "1903";
    this.founder = "Henry Ford";
}
var myFord = new Ford();
// for .. in ciklus
for (var property in myFord) {
    result.innerHTML += myFord[property] + '<br />';
}
// Object.keys() metódus -> tömböt ad vissza
result.innerHTML += '<br />[' +Object.keys(myFord) + ']<br /><br />';
// Object.getOwnPropertyNames(objectname)
function Mustang() {
    this.model = "Mustang";
    this.found = "1964";
    this.nick = "pony car";
}
Mustang.prototype = new Ford();

var fastback = new Mustang();
result.innerHTML += '<b>All properties</b><br />'; 
for(var i in fastback){
    if(fastback.hasOwnProperty(i)){
        result.innerHTML += '[Saját] '+i+'<br />';
    } else { 
        result.innerHTML += '[Örökölt] '+i+'<br />';
    }
}
result.innerHTML += '<b>Own properties</b><br />'; 
result.innerHTML += Object.getOwnPropertyNames(fastback) + '<br />';