Namespaces in node.js with require

Question

I am playing around and learning about vows with a personal project. This is a small client side library, with testing done in vows. Therefore, I must build and test a file that is written like this:

(function(exports) { 
    var module = export.module = { "version":"0.0.1" }; 
    //more stuff
})(this);

In my testing (based off of science.js, d3, etc.) requires that module like so:

require("../module");

I continued to get a "module not defined error" when trying to run the tests, so I went to a repl and ran:

require("../module")

and it returned:

{ module: { version: "0.0.1" } }

I realize I could do something like:

var module = require("../module").module;

but feel like I am creating a problem by doing it that way, especially since the libraries that I based this project on are doing it in the format I described.

I would like for my project to behave similar to those which I based it off of, where:

require("../module");

creates a variable in this namespace:

module.version; //is valid.

I have seen this in a variety of libraries, and I am following the format and thought process to the T but believe I might be missing something about require behavior I don't know about.

Answer 1

There is no problem creating it this way. Modules define what they return in the module.exports object. By the way, you don't actually need self executing functions (SEF), there is no global leakage like in browsers :-)

Examples

module1.js:

module.exports = {
    module: { 'version': '0.1.1' }
};

main.js:

var module1 = require( './module1.js' );
// module1 has what is exported in module1.js

---

Once you've understood how this works, you can easily export the version number right away if you want to:

module1.js:

module.exports = '0.1.1';

main.js:

var module1 = require( './module1.js' );
console.log( module1 === '0.1.1' ); // true

---

Or if you want some logic, you can easily extend your module1.js file like this:

module.exports = ( function() {
    // some code
    return version;
} () ); // note the self executing part :-)
// since it's self executed, the exported part
// is what's returned in the SEF

---

Or, as many modules do, if you want to export some utility functions (and keep others "private"), you could do it like this:

module.exports = {
    func1: function() {
        return someFunc();
    },

    func2: function() {},

    prop: '1.0.0'
};

// This function is local to this file, it's not exported
function someFunc() {
}

So, in main.js:

var module1 = require( './module1.js' );
module1.func1(); // works
module1.func2(); // works
module1.prop; // "1.0.0"
module1.someFunc(); // Reference error, the function doesn't exist

Your special case

About your special case, I wouldn't recommend doing it like they're doing.

If you look here: https://github.com/jasondavies/science.js/blob/master/science.v1.js

You see that they're not using the var keyword. So, they're creating a global variable.

This is why they can access it once they require the module defining the global variable.

And by the way, the exports argument is useless in their case. It's even misleading, since it actually is the global object (equivalent of window in browsers), not the module.exports object (this in functions is the global object, it'd be undefined if strict mode were enabled).

Conclusion

Don't do it like they're doing, it's a bad idea. Global variables are a bad idea, it's better to use node's philosophy, and to store the required module in a variable that you reuse.

If you want to have an object that you can use in client side and test in node.js, here is a way:

yourModule.js:

// Use either node's export or the global object in browsers
var global = module ? module.exports : window.yourModule;

( function( exports ) {
    var yourModule = {};
    // do some stuff
    exports = yourModule;
} ( global ) );

Which you can shorten to this in order to avoid creating the global variable:

( function( exports ) {
    var yourModule = {};
    // do some stuff
    exports = yourModule;
} ( module ? module.exports : window.yourModule ) );

This way, you can use it like this on the client-side:

yourModule.someMethod(); // global object, "namespace"

And on the server side:

var yourModule = require( '../yourModule.js' );
yourModule.someMethod(); // local variable :-)

Just FYI, .. means "parent directory". This is the relative path of where to get the module. If the file were in the same directory, you'd use ..