Create Minecraft Server Mods using Node.js style modules

2014/01/03 14:52

During the past year I've been tapping away at ScriptCraft in my spare time. In my day job I started using Node.js a couple of months back. One of the things I love about Node.js is its module system which is based on the CommonJS module spec. The module system used by Node.js is just so simple and elegant and really lends itself to thinking about programming in a more modular way. While ScriptCraft is aimed at younger programmers (or programmers who just prefer to mod Minecraft using Javascript rather than Java), I think modules and thinking about code in a modular way should be part of any novice programming curriculum. Modules shoudn't be an afterthought and Node.js's module system is succint and expressive enough to be understandable by beginning programmers. At the end of the day the difference between these two source files is minimal...

hello-basic.js (traditional javascript)

var salutation = 'Hi ';
function greet( player ){
    player.sendMessage(salutation +;

hello-module.js (modular javascript)

var salutation = 'Hi ';
exports.greet = function( player ){
    player.sendMessage(salutation +;

... In the first example, the greet function is a global named function and the salutation variable becomes a global variable too. In the second example, exports.greet is assigned to a function expression and the salutation variable is private. In a node.js module, everything (functions, variables) is private by default. If you want to make something public you add it to the exports variable which 'exports' all its properties for use by others. I've been programming for 26 years and have programmed in a lot of languages in that time. The node.js module system is the most elegant module system I've yet encountered. It's so good that I decided I had to have it in ScriptCraft. I did some digging and there are a couple of implementations of the commonjs module system , at least one or two available for Rhino, but projects like Narwhal seemed to be too heavyweight for ScriptCraft's needs. All I wanted was the bare bones module loader - not the standard module libraries ('http', 'fs', 'system' etc). Really all I needed was a good working require() function that adhered to the CommonJS module contract and to be able to export stuff using exports and module.exports. After some hacking, I got a bare-bones module loader part working recently. It works in Java's javax.scripting JS Engine and conforms to the CommonJS module contract. ScriptCraft modules that reside in the scriptcraft/plugins directory will be loaded automatically at Server start-up and any exports will become global variables - this is obviously different from how Node.js modules work but it's a convenience for novice programmers who just want to write functions and be able to execute them at the in-game or server console prompt. Modules in the scriptcraft/plugins directory are also auto-loaded and auto-globals to be backward compatible with how ScriptCraft used to work (all .js files autoloaded at startup - dependencies between modules was a bit problematic). ScriptCraft modules that reside in the scriptcraft/modules directory behave pretty much identically to Node.js modules. For example to use the utils module (which resides in scriptcraft/modules/utils/

var utils = require('utils');
var player = utils.player('walterh');
player.sendMessage('Hello ');

... this style of javascript coding should be familiar to Node.js programmers and I think it's a good idea to expose younger programmers to modules early in the course of learning programming. Thinking about how to decompose a big problem (how do I create a complex minecraft mod) into smaller problems and solving each problem in turn using distinct modules, is a good skill to have and the CommonJS module system is a superb tool for thinking about problems in a modular way. Variables, Functions, Looping, Conditionals, Modules and the distinction between private and public data and functions are all important basic concepts in teaching programming. Most of us who learned Javascript had to overlook the lack of a module system and the syntactic ju-jitsu required to get privacy, but now at least (on the server-side) there's a great module system in CommonJS. I'm going to stick my neck out here and predict that in the long run, any Javascript framework that doesn't use the CommonJS module system will eventually lose out to JS frameworks which do use CommonJS modules.

Things will be better for the Javascript programmers of tomorrow.


ScriptCraft, Nodejs, Javascript