module.export-ing 从另一个文件后函数未定义

Question

我有一个需要 player.js 的 nodeJS 应用程序。在player.js 中我定义了Player 并添加了Player.updatePacket 方法，但是当我在main.js 中需要它并创建一个播放器实例时，player.updatePacket 是未定义的。

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);

我尝试将导出语句移动到player.js 的底部并将updatePacket: function() {/*function contents*/} 放入tmp 对象中，但我仍然得到同样的错误。任何帮助或解释表示赞赏。

Answer 1

试试这个

播放器.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);

这种解释可能过于简单，但在 JS 中，“类”是函数，为了给类添加方法，我们必须将它们添加到原型中。当我们在该类上使用“new”时，它会继承其原型链上存在的所有方法。

这个链接可能被证明是一个更好的解释 https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/prototype

Answer 2

您的模块的导出是一个具有.Player 属性的对象：

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

因此，您需要在需要 Player 对象时访问该属性：

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

（首选）替代方法是将Player 设为导出对象本身（“别名”）：

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

如果您想使用默认对象以外的其他对象，则不能使用exports，而必须使用assign to module.exports。