sealingObject.js

const user = {
  firstName: 'Akash'
}

// Sealing Object
Object.seal(user)
console.log(Object.isSealed(user)) // true

// Configurable == false ( we can't add or delete properties )
const descriptor = Object.getOwnPropertyDescriptor(user, 'firstName')
console.log(descriptor.configurable) // false 
console.log(Object.isExtensible(user)) // false

user.lastName = 'Rajvanshi'
console.log('lastName' in user) // false

delete user.firstName
console.log('firstName' in user) // true

// Only we can do is write existing properties 
user.firstName = 'Abha';
console.log(user.firstName) // Abha