es6.class.extends.js

class User {
  constructor(name) {
    this.name = name;
  }

  say(msg) {
    console.log(this.name + ' say: ' + msg);
  }
}

class Admin extends User {
  constructor(...args) {
    super(...args);
  }

  // расширим метод say()
  say(...args) {
    console.log('Attention!!!');
    super.say(...args);
  }
}

var user = new User('user1');

user.say('hello!');

// user1 say: hello!

var admin = new Admin('admin1');

admin.say('welcome!');

// Attention!!!
// admin1 say: welcome!