在Node.js中创建模块的副本而不是实例

Question

this would be my first question ever on stackoverflow, hope this goes well. I've been working on a game (using corona SDK) and I used Node.js to write a small little server to handle some chat messages between my clients, no problems there. Now I'm working on expanding this little server to do some more, and what I was thinking to do is create an external file (module) that will hold an object that has all the functions and variables I would need to represent a Room in my games "Lobby", where 2 people can go into to play one against the other, and each time I have 2 players ready to play, I would create a copy of this empty room for them, and then initialize the game in that room. So I have an array in my main project file, where each cell is a room, and my plan was to import my module into that array, and then I can init the game in that specific "room", the players would play, the game will go on, and all would be well... but... my code in main.js:

var new_game_obj = require('./room.js');

games[room_id] = new_game_obj();

games[room_id].users = [user1_name,user2_name];

Now, in my room.js, I have something of the sort:

var game_logistics = {};

game_logistics.users = new Array();

game_logistics.return_users_count = function(){
    return game_logistics.users.length;
}

module.exports = function() {
    return game_logistics;
}

So far so good, and this work just fine, I can simply go:

games[room_id].return_users_count()

And I will get 0, or 1, or 2, depending of course how many users have joined this room. The problems starts once I open a new room, since Node.js will instance the module I've created and not make a copy of it, if I now create a new room, even if I eliminated and/or deleted the old room, it will have all information from the old room which I've already updated, and not a new clean room. Example:

var new_game_obj = require('./room.js');

games["room_1"] = new_game_obj();
games["room_2"] = new_game_obj();

games["room_1"].users = ["yuval","lahav"];

_log(games["room_1"].return_user_count()); //outputs 2...
_log(games["room_2"].return_user_count()); //outputs 2...

Even doing this:

var new_game_obj = require('./room.js');
games["room_1"] = new_game_obj();

var new_game_obj2 = require('./room.js');
games["room_2"] = new_game_obj2();

games["room_1"].users = ["yuval","lahav"];

_log(games["room_1"].return_user_count()); //outputs 2...
_log(games["room_2"].return_user_count()); //outputs 2...

Gives the same result, it is all the same instance of the same module in all the "copies" I make of it. So my question as simple as that, how do I create a "clean" copy of my original module instead of just instancing it over and over again and actually have just one messy room in the end?

Answer 1

What you're doing is this (replacing your require() call with what gets returned);

var new_game_obj = function() {
    return game_logistics;
}

So, every time you call new_game_obj , you return the same instance of game_logistics .

Instead, you need to make new_game_obj return a new instance of game_logistics ;

// room.js
function Game_Logistics() {
    this.users = [];

    this.return_users_count = function(){
        return this.users.length;
    };
}

module.exports = function() {
    return new Game_Logistics(); 
}

This is quite a shift in mentality. You'll see that we're using new on Game_Logistics in module.exports to return a new instance of Game_Logistics each time it's called.

You'll also see that inside Game_Logistics , this is being used everywhere rather than Game_Logistics ; this is to make sure we're referencing the correct instance of Game_Logistics rather than the constructor function.

I've also capitalized your game_logistics function to adhere to the widely-followed naming convention that constructor functions should be capitalized ( more info ).

Taking advantage of the prototype chain in JavaScript is recommended when you're working with multiple instances of functions. You can peruse various articles on "javascript prototypical inheritance* (eg this one ), but for now, the above will accomplish what you need.