Mastering JavaScript

Chapter 9
Creating modules
Node modules can be either single files or directories containing one or more files.
It's usually a good idea to create a separate module directory. The file in the module
directory that will be evaluated is normally named index.js. A module directory
can look as follows:
node_project/src/nav
--- >index.js
In your project directory, the nav module directory contains the module code.
Conventionally, your module code needs to reside in the index.js file—you can
change this to another file if you want. Consider this trivial module called geo.js:
exports.area = function (r) {
return 3.14 * r * r;
};
exports.circumference = function (r) {
return 3.14 * 3.14 * r;
};
You are exporting two functions via exports. You can use the module using the
require function. This function takes the name of the module or system path to the
module's code. You can use the module that we created as follows:
var geo = require('./geo.js');
console.log(geo.area(2));
As we are exporting only two functions to the outside world, everything else
remains private. If you recollect, we discussed the module pattern in detail—Node
uses CommonJS modules. There is an alternative syntax to create modules as well.
You can use modules.exports to export your modules. Indeed, exports is a helper
created for modules.exports. When you use exports, it attaches the exported
properties of a module to modules.exports. However, if modules.exports already
has some properties attached to it, properties attached by exports are ignored.
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