let person = {
firstName: "Zhentian",
lastName: "Wan"
};
/*Object.freeze() makes object cannot be updated, added or deleted*/
let freezePerson = Object.freeze(person);
freezePerson.address="Finland"; // Cannot add property address, object is not extensiable.
console.log(freezePerson.firstName); // Zhentian
freezePerson.firstName = "John"; //Cannot assing to read only property 'firstName'
/*Seal, property can be udpated, but cannot be delted or added*/
let sealPerson = Object.seal(person);
sealPerson.firstName = "Answer"; // works!
console.log(sealPerson.firstName);
sealPerson.address="Finland"; // Cannot add property address, object is not extensible
console.log(sealPerson.address);
