Question

我在我的一个函数中使用了一个socket.io监听器来监听“失败者”事件，告诉客户另一个客户赢了。但是，在socket.on函数内部，我不能使用“this”关键字来讨论我的客户端，因为这指的是套接字本身。我是以错误的方式来做这件事的吗？或者可以通过其他方式访问客户端对象，例如super？

            socket.on('loser', function() {
                //Remove all current objects then restart the game.
                //THIS PART DOESN'T WORK, SINCE 'THIS' NO LONGER REFERS TO 
                //THE GAME OBJECT, BUT INSTEAD REFERENCES THE SOCKET LISTENER.
                for(var i = 0; i < this.board.objects.length; i++)
                {
                    this.board.remove(this.board.objects[i]);
                }
                //WORKS AS EXPECTED FROM HERE ON...
                Game.setBoard(1, new TitleScreen(gameType,
                        "Loser!",
                         "Press Space to Play Again", 
                     playGame));                    
            });

Answer 1

函数不包含有关引用它们的对象的任何信息，您可以使用.bind()将函数绑定到对象，然后再传递它：

socket.on('loser', function() {
    //Remove all current objects then restart the game.
    //THIS PART DOESN'T WORK, SINCE 'THIS' NO LONGER REFERS TO 
    //THE GAME OBJECT, BUT INSTEAD REFERENCES THE SOCKET LISTENER.
    for (var i = 0; i < this.board.objects.length; i++) {
        this.board.remove(this.board.objects[i]);
    }
    //WORKS AS EXPECTED FROM HERE ON...
    Game.setBoard(1, new TitleScreen(gameType, "Loser!", "Press Space to Play Again",
    playGame));
}.bind(this));

Answer 2

在浏览器版本中，执行此操作的常用方法是在输入函数之前设置var that = this;之类的变量，然后改用that。

然而，ECMAScript5引入了bind()，这可以防止this的值丢失。当然，在NodeJS中使用它是安全的（不像在浏览器领域，你必须支持旧的浏览器）。

socket.on('loser', (function() {
    //Remove all current objects then restart the game.
    for (var i = 0; i < this.board.objects.length; i++) {
        this.board.remove(this.board.objects[i]);
    }
    //WORKS AS EXPECTED FROM HERE ON...
    Game.setBoard(1, new TitleScreen(gameType, "Loser!", "Press Space to Play Again", playGame));
}).bind(this));

有关详细信息，请参阅https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Function/bind

Answer 3

这样的事情出了什么问题？

var self = this;
socket.on('loser', (function() {
    //Remove all current objects then restart the game.
    for (var i = 0; i < self.board.objects.length; i++) {
        self.board.remove(self.board.objects[i]);
    }
}

在Socket.io中使用此关键字的功能

3 个答案: