How to add getter/setter methods to ES6 classes after the class is created

gistfile1.js

// Also works for normal methods
class User {
  constructor (first, last) {
    this.firstName = first;
    this.lastName = last;
  }
}

Object.defineProperty(User.prototype, 'name', {
  get: function () { 
    return `${this.firstName} ${this.lastName}` 
  },
  set: function (name) {
    let split = name.split(' ');
    this.firstName = split[0];
    this.lastName = split[1];
  }
});

let user = new User('jon', 'abrams');
console.log(user.name); // outputs "jon abrams"

user.name = "Jon Abrams";
console.log(user.name); // outputs "Jon Abrams"

Thanks! It helped me resolve kata. Bad what I can not myself come to this solution.