function Person(name, surname) {
	this.name = name;
	this.surname = surname;
	
	Object.seal(this);
}


var person = new Person("Jan", "Kowalski");

console.log(delete person.name);		// wynik:		false
console.log(person.name);			// wynik:		"Jan"


if (!Object.isSealed(person)) {
	delete person.name;
}