sag1v

function PaidPlayer(userName, score, balance) {
  this.balance = balance;
  /* we are calling "Player" without the "new" operator
  but we use the "call" method,
  which allows us to explicitly pass a ref for "this".
  Now the "Player" function will mutate "this"
  and will populate it with the relevant properties */
  Player.call(this, userName, score);
}

sag1v

function double(num) {
    return num * 2;
}

double.someProp = 'Hi there!';

double(5); // 10
double.someProp // Hi there!

double.prototype // {}

sag1v

player1 {
  userName: "sag1v",
  score: 700,
  __proto__: playerFunctions {
     setScore: ƒ
  }
}

paidPlayer {
  userName: "sarah",

sag1v

const playerFunctions = {
  setScore(newScore) {
    this.score = newScore;
  }
}

function createPlayer(userName, score) {
  const newPlayer = Object.create(playerFunctions);
  newPlayer.userName = userName;
  newPlayer.score = score;

sag1v

Player {
  userName: "sag1v",
  score: 700,
  __proto__: Player.prototype {
    setScore: ƒ
  }
}

PaidPlayer {
  userName: "sarah",

sag1v

Player {
  userName: "sag1v",
  score: 700,
  __proto__: Player.prototype
}

Player {
  userName: "sarah",
  score: 900,
  __proto__: Player.prototype

sag1v

// link PaidPlayer.prototype object to Player.prototype object
Object.setPrototypeOf(PaidPlayer.prototype, Player.prototype);

sag1v

function double(num){
    return num * 2;
}

double.toString() // where is this method coming from?

Function.prototype // {toString: f, call: f, bind: f}

double.hasOwnProperty('name') // where is this method coming from?

sag1v

function createPlayer(userName, score) {
  const newPlayer = {
    userName,
    score,
    setScore(newScore) {
      newPlayer.score = newScore;
    }
  }
  return newPlayer;
}

sag1v

class PaidPlayer extends Player {
  constructor(userName, score, balance) {
    // "this" is uninitialized yet...
    // super refers to Player in this case
    super(userName, score);
    // under the hood super is implemented with Reflect.construct
    // this = Reflect.construct(Player, [userName, score], PaidPlayer);
    this.balance = balance;
  }