功能未定義後module.export從另一個文件

Question

我有一個nodeJS應用程序需要player.js。在player.js中，我定義了Player並添加了方法Player.updatePacket，但是當我需要它在main.js中並創建播放器實例時，player.updatePacket未定義。

player.js：

module.exports.PLAYER_LIST = {}; 
var Player = exports.Player = {} 

//constructor 
Player.create = function(id) { 
    var tmp = { 
     id: id, 
     x: 0, 
     y: 0 
    }; 
    PLAYER_LIST[id] = tmp; 
    return tmp; 
} 

Player.updatePacket = function() { 
    return { 
     id: this.id, 
     x: this.x, 
     y: this.y 
    } 
} 

main.js：

var Player = require('./player.js') 

//get called by socket.io when a client connects 
//didn't include socket.io setup in example for brevity, but this function 
//is called as expected.  
io.sockets.on('connection', function(socket){ 
    var player = new Player(socket.id) 

}); 

setInterval(function() { 
    var dataArr = []; 
    for(var i in Player.PLAYER_LIST) { 
     var player = Player.PLAYER_LIST[i]; 
     console.log(player); //this logs: [Function] 
     dataArr += player.updatePacket(); //throws TypeError: not a function 
    } 
    broadcast("update", dataArr); 
}, 1000/25); 

我試圖移動出口語句的player.js底部，並把updatePacket: function() {/*function contents*/}在TMP對象，我仍然得到同樣的錯誤。任何幫助或解釋讚賞。

Answer 1

你的模塊的出口是有一個.Player屬性的對象：

var Player = exports.Player = {}; 
//   ^^^^^^^^^^^^^^^^ 

這樣，你需要的時候，你希望你的Player對象訪問屬性：

/* main.js */ 
var Player = require('./player.js').Player; 
//         ^^^^^^^ 

的（優選）替代方案是使Player的出口對象本身（「別名」）：

/* player.js */ 
var Player = exports; // or = module.exports; 

如果您想要使用除默認對象之外的其他內容，則不能使用exports，但必須使用assign to module.exports。

Answer 2

試試這個

Player.js

var PlayerList = module.exports.PLAYER_LIST = {}; 
var Player = module.exports.Player = function(id) { 
    this.id = id; 
    this.x = 0; 
    this.y = 0 
    PlayerList[id] = this; 
}; 

Player.prototype.updatePacket = function() { 
    return { 
     id: this.id, 
     x: this.x, 
     y: this.y 
    } 
}; 

Main.js

var Player = require('./player.js').Player; 
var PLAYER_LIST = require('./player.js').PLAYER_LIST; 

io.sockets.on('connection', function(socket){ 
    var player = new Player(socket.id) 

}); 

setInterval(function() { 
    var dataArr = []; 
    for(var i in PLAYER_LIST) { 
     var player = PLAYER_LIST[i]; 
     console.log(player); 
     dataArr.push(player.updatePacket()); //note that it is push not += when adding items to an array 
    } 
    broadcast("update", dataArr); 
}, 1000/25); 

這種解釋可能是一個過於簡單化，但在JS， '類' 是功能，爲了增加方法放到類上，我們必須將它們添加到原型中。當我們在該類上使用'new'時，它會繼承其原型鏈上存在的所有方法。

此鏈接可能被證明是一個更好的解釋 https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/prototype