First, note that you're using new with User and Person, but your code throws away the object new creates by returning a different object from those functions. So new User() and User() do exactly the same thing.
And that's largely the reason you don't have access to User features in Person, because the prototype of the object returned isn't User.prototype, it's Object.prototype.
If you don't want new...
...you want to create your "person" objects so they're backed by User directly (or via Object.create(User())):
var Game = (function() {
var User = function() { // <== Note the `var`
var username;
return {
setUsername: function(newUsername) {
username = newUserName;
},
getUsername: function() {
return username;
}
}
};
var Player = function() { // <== Note the `var`
var score = 0;
// Create the player, either using a User directly:
var player = User();
// ...or by using a User as a prototype:
var player = Object.create(User());
player.getScore = function() {
return score;
};
player.play = function() {
score = Math.round(Math.random() * 100);
};
return player;
};
return {
player1: Player(), // No `new`
player2: Player()
};
});
var game = new Game();
game.player1.setUsername('alex');
game.player2.setUsername('tony');
game.player1.play();
game.player2.play();
console.log(game.player1.getUsername() + ': ' + game.player1.getScore());
console.log(game.player2.getUsername() + ': ' + game.player2.getScore());
That keeps the username and score properties private, as in your original code.
If you want to use new
...then you probably want the fairly standard pattern I describe in this answer, which looks like this applied to your code:
var Game = (function() {
var User = function() {
};
User.prototype.setUsername = function(newUsername) {
this.username = newUserName;
};
User.prototype.getUsername = function() {
return this.username;
};
var Player = function() {
this.score = 0;
};
Player.prototype = Object.create(User.prototype);
Player.prototype.constructor = Player;
Player.prototype.getScore = function() {
return this.score;
};
Player.prototype.play = function() {
this.score = Math.round(Math.random() * 100);
};
return {
player1: new Player(),
player2: new Player()
};
});
var game = new Game();
game.player1.setUsername('alex');
game.player2.setUsername('tony');
game.player1.play();
game.player2.play();
console.log(game.player1.getUsername() + ': ' + game.player1.getScore());
console.log(game.player2.getUsername() + ': ' + game.player2.getScore());
Or in ES2015:
var Game = (function() {
class User {
setUsername(newUsername) {
this.username = newUserName;
}
getUsername() {
return this.username;
}
}
class Player extends User {
constructor() {
this.score = 0;
}
getScore() {
return this.score;
}
play() {
this.score = Math.round(Math.random() * 100);
}
}
return {
player1: new Player(),
player2: new Player()
};
});
var game = new Game();
game.player1.setUsername('alex');
game.player2.setUsername('tony');
game.player1.play();
game.player2.play();
console.log(game.player1.getUsername() + ': ' + game.player1.getScore());
console.log(game.player2.getUsername() + ': ' + game.player2.getScore());
Note that in both of those second two examples, username and score are no longer private. That said, even private variables in languages with built-in privacy like Java are trivially used outside of the private scope, via the reflection features of those languages.
In ES2015, we can use a WeakMap to get privacy as good as your original code's is:
var Game = (function() {
var UserNames = new WeakMap();
class User {
setUsername(newUsername) {
UserNames.set(this, newUsername);
}
getUsername() {
return UserNames.get(this);
}
}
var PlayerScores = new WeakMap();
class Player extends User {
constructor() {
PlayerScores.set(this, 0);
}
getScore() {
return PlayerScores.get(this);
}
play() {
PlayerScores.set(this, Math.round(Math.random() * 100));
}
}
return {
player1: new Player(),
player2: new Player()
};
});
var game = new Game();
game.player1.setUsername('alex');
game.player2.setUsername('tony');
game.player1.play();
game.player2.play();
console.log(game.player1.getUsername() + ': ' + game.player1.getScore());
console.log(game.player2.getUsername() + ': ' + game.player2.getScore());
That doesn't cause a memory leak, because when a User or Person object is no longer referenced by anything other than the WeakMap, the WeakMap lets go of it and it can be garbage collected.
