函数在模块后不确定

Question

我有一个需要 player.js的nodejs应用程序。在player.js中，我定义了Player并添加方法Player.updatePacket，但是当我在main.js中需要它并创建播放器实例时，player.updatePacket不确定。

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至player.js的底部并将updatePacket: function() {/*function contents*/}放在TMP对象中，但我仍然遇到相同的错误。感谢任何帮助或解释。

Answer 1

尝试此

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);

此解释可能是一个过度简化的，但是在JS中，"类"是函数，为了将方法添加到类中，我们必须将它们添加到原型中。当我们在该类上使用"新"时，它继承了其原型链上存在的所有方法。

此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/objects/object/prototype

Answer 2

模块的导出是具有.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;
//                                 ^^^^^^^

（优选的）替代方案是使Player导出对象本身（一个"别名"）：

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

如果要使用默认对象以外的其他内容，则不能使用exports，但必须分配给module.exports。