Singleton.js

class User {
  constructor(firstName, lastName) {
    if (User.exists) {
      return User.instance
    }
    
    this._firstName = firstName
    this._lastName = lastName
    
    User.exists = true
    User.instance = this
      
    return this

  }
  
  get firstName() {
    return this._firstName
  }
  
  get lastName() {
    return this._lastName
  }
  
  get user() {
    return {
      firstName: this._firstName,
      lastName: this._lastName
    }
  }
}


const FirstUser = new User('thomas', 'd')
const SecondUser = new User('alexandra', 'c')

console.log(FirstUser)
console.log(SecondUser)