我正在尝试创建一个简单的 JavaScript 继承,但我错过了一些东西,我需要你的帮助。
基本上,我有一个可以拥有用户名的User
。我还有一个继承自 User 的 Player,可以有分数并进行游戏。
var Game = (function () {
User = function () {
var username;
return {
setUsername: function (newUsername) {
username = newUserName;
},
getUsername: function () {
return username;
}
}
};
Player = function () {
var score = 0;
return {
getScore: function () {
return score;
},
play: function () {
score = Math.round(Math.random()*100);
}
};
};
Player.prototype = new User();
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());
我遇到的问题来自于我无法从播放器中的用户访问该方法。但我不确定如何访问它们。
这是一个jsfiddle:https://jsfiddle.net/3xsu8pdy/
有什么想法吗? 谢谢。
谢谢。
最佳答案
首先,请注意,您将 new
与 User
和 Person
一起使用,但您的代码会丢弃对象 new
通过从这些函数返回不同的对象来创建。因此,new User()
和 User()
执行完全相同相同的操作。
这很大程度上是您无法访问 Person
中的 User
功能的原因,因为返回的对象的原型(prototype)不是 User.prototype
,它是Object.prototype
。
如果您不想要新的
...
...您想要创建“person”对象,以便它们直接由 User
支持(或通过 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());
这使得 username
和 score
属性保持私有(private),就像在原始代码中一样。
如果你想使用new
...那么您可能需要相当标准的模式 I describe in this answer ,这看起来适用于您的代码:
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());
或者在 ES2015 中:
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());
请注意,在后两个示例中,username
和 score
不再是私有(private)的。也就是说,即使像 Java 这样具有内置隐私的语言中的私有(private)变量,也可以通过这些语言的反射功能在私有(private)范围之外使用。
在 ES2015 中,我们可以使用 WeakMap
来获得与原始代码一样好的隐私:
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());
这不会导致内存泄漏,因为当 User
或 Person
对象不再被 WeakMap
以外的任何对象引用时,WeakMap
放开它,它可以被垃圾回收。
关于Javascript 继承与揭示原型(prototype)设计模式,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/34681532/