.js

var user = {
  create: function create() {
    return this.constructor.apply(Object.create(this), arguments)
  },
  constructor: function User(firstname, lastname) {
    this.firstname = firstname
    this.lastname = lastname
    return this
  },
  getName: function getName() {
    return this.firstname + " " + this.lastname
  },
}

user.create("John", "Doe").getName() // "John Doe"