Directories as modules

A module can contain a whole directory structure full of stuff. Stuff here is a technical term referring to internal file modules, data files, template files, documentation, tests, assets, and more. Once stored within a properly constructed directory structure, Node.js will treat these as a module that satisfies a require('moduleName') call.

This may be a little confusing because the word module is being overloaded with two meanings. In some cases, a module is a file, and in other cases, a module is a directory containing one or more file modules.

In most cases, a directory-as-module contains a package.json file. This file contains data about the module (known as package) that Node.js uses while loading the module. The Node.js runtime recognizes these two fields:

{ name: "myAwesomeLibrary", 
  main: "./lib/awesome.js" }

If this package.json file is in a directory named awesomelib, then require('./awesomelib') will load the file module in ./awesomelib/lib/awesome.js. 

If there is no package.json, then Node.js will look for either index.js or index.node. In such a case, require('./awesomelib') will load the file module in ./awesomelib/index.js.

In either case, the directory module can easily contain other file modules. The module that's initially loaded would simply use require('./anotherModule') one or more times to load other, private modules.

The npm package management system can recognize a lot more data in the package.json file. That includes the package name, its author, the home page URL, the issue-queue URL, package dependencies, and more. We'll go over this later.