在Socket.io函數中使用此關鍵字

Question

我在其中一個函數中使用socket.io偵聽器，以偵聽“失敗者”事件，以告知客戶端另一個客戶端獲勝。 但是，當在socket.on函數內部時，我不能使用“ this”關鍵字來談論我的客戶端，因為這是指套接字本身。 我會以錯誤的方式處理嗎？ 還是可以通過其他方式（例如超級）訪問客戶端對象？

            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

函數不包含有關引用它們的對象的任何信息，可以在傳遞函數之前使用.bind()將函數綁定到對象：

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

在瀏覽器領域，執行此操作的常用方法是設置一個變量，例如var that = this; 在輸入功能之前that改用該功能。

但是，ECMAScript5引入了bind() ，它使您可以防止丟失this值。 當然，在NodeJS中，使用它是安全的（不同於在瀏覽器領域，必須支持較舊的瀏覽器）。

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));​

有關更多信息，請參見https://developer.mozilla.org/zh-CN/docs/JavaScript/Reference/Global_Objects/Function/bind

Answer 3

這樣的事情怎么了？

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]);
    }
}