Node.JS Module Patterns

Using Simple Examples

Darren DeRidder / @73rhodes

Modules for `n00bs`

Node.JS - a Common.JS Module Implementation
Your code uses require to include modules.
Modules use exports to make things available.

Common.JS

An ecosystem for JavaScript outside the browser

Modules
Promises
Binary
Filesystem
Console
System
Testing

Kevin Dangoor, What Server Side JavaScript Needs

"What I’m describing here is not a technical problem. It’s a matter of people getting together and making a decision to step forward and start building up something bigger and cooler together."

Common.JS Implementations

MongoDB
CouchDB
SproutCore
Node.JS

The Simplest Module


 
    // hello.js
    console.log('Hello World');


 
    // app.js
    require('./hello.js');

implied facepalm...

Pattern 1: Define a Global


 
    // foo.js
    foo = function () {
      console.log('foo!');
    }


 
    // app.js
    require('./foo.js');
    foo();

don't pollute the global space

Pattern 2: Export an Anonymous Function


 
    // bar.js
    module.exports = function () {
      console.log('bar!');
    }


 
    // app.js
    var bar = require('./bar.js');
    bar();

Pattern 3: Export a Named Function


 
    // fiz.js
    exports.fiz = function () {
      console.log('fiz!');
    }


 
    // app.js
    var fiz = require('./fiz.js').fiz;
    fiz();

Pattern 4: Export an Anonymous Object


 
    // buz.js
    var Buz = function () {};

    Buz.prototype.log = function () {
      console.log('buz!');
    };

    module.exports = new Buz();


 
    // app.js
    var buz = require('./buz.js');
    buz.log();

Pattern 5: Export a Named Object


 
    // baz.js
    var Baz = function () {};

    Baz.prototype.log = function () {
      console.log('baz!');
    };

    exports.Baz = new Baz();


 
    // app.js
    var baz = require('./baz.js').Baz;
    baz.log();

Pattern 6: Export an Anonymous Prototype


 
    // doo.js
    var Doo = function () {};

    Doo.prototype.log = function () {
        console.log('doo!');
    }

    module.exports = Doo;


 
    // app.js
    var Doo = require('./doo.js');
    var doo = new Doo();
    doo.log();

Pattern 7: Export a Named Prototype


 
    // qux.js
    var Qux = function () {};

    Qux.prototype.log = function () {
      console.log('baz!');
    };

    exports.Qux = Qux;


 
    // app.js
    var Qux = require('./qux.js').Qux;
    var qux = new Qux();
    qux.log();

Pros and Cons

Named exports - one module, many exported things

Anonymous exports - simpler client interface

module.exports
VS
exports

exports VS. module.exports

exports is an alias to module.exports.
node automatically creates it as a convenient shortcut.
For assigning named properties, use either one.


 
> module.exports.fiz = "fiz";
> exports.buz = "buz";
> module.exports === exports;
true

Warning

Assigning anything to exports directly (instead of exports.something) will overwrite the exports alias.


 
> module.exports.qux = "qux";
> exports
{ qux: "qux" }
> exports === module.exports
true
> exports = "wobble wibble wubble!";
> exports === module.exports
false
> exports
"wobble wibble wubble!"
> module.exports
{ qux: "qux" }
// module.exports is canonical

Thanks!

http://darrenderidder.github.io/talks/ModulePatterns