Access global variable outside of anonymous function in JavaScript using require

Question

I'm developing a HTML5 real-time multiplayer game and I have a game_core.js file that runs the game physics using the p2 library. I would like to run this file both on the client, to make prediction, and on the authoritative server. Here's the constructor and module.exports:

function gameCore() {
    this.world = new p2.World({gravity:[0, 0]});
    this.players = {};
    this.step = 1/60;
}

...

module.exports = gameCore;

Since I'm loading the p2.js file inside index.html

<script type="text/javascript" src="lib/p2.js"></script>
<script type="text/javascript" src="game_client.js"></script>
<script type="text/javascript" src="game_core.js"></script>

the constructor finds the p2 object and everything works fine. But my problem is when I try to run this file on the server, because I can't find a proper way to access the p2 object, that is a global variable on game_server.js:

var
    io              = require('socket.io'),
    express         = require('express'),
    UUID            = require('node-uuid'),
    p2              = require('p2'),
    verbose         = false,
    http            = require('http'),
    app             = express(),
    config          = require('./config.json'),
    gameCore        = require('./game_core.js'),
    server          = http.createServer(app);

var world = new gameCore();

I get this error:

this.world = new p2.World({gravity:[0, 0]});
                         ^
ReferenceError: p2 is not defined

If I create a p2 property on gameCore, leave world as null on the constructor, assign the global p2 to gameCore's p2 and then assign the correct value to world using a init function

function gameCore() {
    this.p2 = null;
    this.world = null;
    this.players = {};
    this.step = 1/60;
}

gameCore.prototype.init = function() {   
    this.world = new this.p2.World({gravity:[0, 0]});
}

it works, but since I need to do this on other classes of gameCore I get a stack overflow. And if I use

var p2 = require('p2');

on gameCore it works, but the client complains about using require.

I'm new to JavaScript, but I've looked at closure, anonymous functions and many similar doubts. Unfortunately I couldn't solve this issue yet.

@tom, that solved my problem, thank you! But if anyone knows another solution without bundling my scripts in one single file, I would like to know. — Matheus Camargo
– Matheus Camargo, Commented May 27, 2015 at 11:38
Is there a reason you don't want to bundle your scripts? In development you are supposed to keep them all separated out. You only bundle them when you're ready to test or ship. The runtime is exactly the same as if they were in different files except its slightly faster because it only has to get at one file. — t3dodson
– t3dodson, Commented Jun 1, 2015 at 17:17
if its the time it takes to call the bundle command I suggest looking into grunt.js its a tool that can automate the task. You can set your project to bundle everytime you save a file. — t3dodson
– t3dodson, Commented Jun 1, 2015 at 17:18
@tom Oh, grunt.js is what I wanted in order to automate this bundling task. Thank you again! — Matheus Camargo
– Matheus Camargo, Commented Jun 2, 2015 at 15:46

t3dodson · Accepted Answer · 2015-05-27 16:31:46Z

1

browserify lets you use require within your client js files.

Also you need game_core.js require p2 if you want to use p2 in the constructor.

Your client file using browserify should look like this

<script src="bundle.js"></script> <!-- browserify p2 game_core.js config.json --->
<script>
  var p2 = require('p2 ');
  var game_core= require('game_core.js');
  var config= require('config.json');
 /* ... */
</script>

edited May 27, 2015 at 16:31

answered May 26, 2015 at 23:33

t3dodson

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