Object Mutation in Javascript

object-mutation.js

const user = {
  age: 22,
  gender: 'male',
  address: {
    city: 'Kyiv'
  }
}

// Copying objects
const user2 = user;                            // assignment of reference
const user3 = Object.assign({}, user)          // shallow copying
const user4 = { ...user }                      // shallow copying (shorter)
const user5 = JSON.parse(JSON.stringify(user)) // deep cloning/copying

console.log(user2.age, user2.gender, user2.address.city) // 22, 'male', 'Kyiv'

// All level mutation - assignment of reference
user2.age = 33
user2.gender = 'female'
user2.address.city = 'Kharkiv'
console.log(user.age, user.gender, user.address.city) // 33, 'female', 'Kharkiv'

// Only first level mutation - shallow copying
user3.age = 44
user3.gender = 'male'
user3.address.city = 'Odesa'
console.log(user.age, user.gender, user.address.city) // 33, 'female', 'Odesa'

// Only first level mutation - shallow copying (shorter)
user4.age = 55
user4.gender = 'male'
user4.address.city = 'Lviv'
console.log(user.age, user.gender, user.address.city) // 33, 'female', 'Lviv'

// No mutation - deep cloning/copying
user5.age = 0
user5.gender = 'none'
user5.address.city = 'none'
console.log(user.age, user.gender, user.address.city) // 33, 'female', 'Lviv'