Node.js has its own package manager, Node Packaged Modules (npm), which allows you to install third party modules and their dependencies. Modules are either installed locally, inside a directory, or globally, that is, on a location typically available as part of your path so they can be globally accessed.

Most Node.js applications make extensive use of modules. A module is basically application code described by a package.json file. The code and packages.json files can be in a directory, a Git repository, a compressed tarball, or a URI to a compressed tarball.

A package or module can be published to the npm registry. Once published, it can be referred to by a <name>@<version> string, where <version> can also be a tag or defaults to the latest tag if omitted. A module can be installed by doing the following:

$ npm install [-g] <module reference>

In this case, <module reference> is one of the following:

• A directory containing the packages.json file and the code itself
• A compressed tarball of the above, or a URI to it
• A Git repository with the packages.json file and the code itself
• A <name>@<version> string that represents a module published in the npm registry

In the previous command, the optional -g is specifying a global install.

To create a package we can, for example, use the following helloworld.js code:

var http = require('http'); 
http.createServer(function (request, response) { 
    response.writeHead(200, {'Content-Type': 'text/plain'}); 
    response.end('Hello World
'); 
}).listen(8080); 
console.log('Server started'); 

You will also need to use its corresponding packages.json description file:

{ 
  "name": "nodejs-helloworld",                                               
  "version": "1.0.0",                                                            
  "description": "An example node.js hello world server",                        
  "main": "helloworld.js",                                                            
  "author": "Alex Gonzalez <[email protected]>",                           
  "license": "ISC"                                                               
} 

The creation of a packages.json file can be automated with the npm tool by doing the following from the same directory:

$ npm init

To try the module out, we can install it globally with the following:

$ npm install -g .

The . in the previous command specifies the current directory. It can be executed with the following:

$ nodejs helloworld.js

Directing a browser to localhost:8080 displays the Hello World message.

Once it works, we can publish it to the npm registry with the following:

$ npm adduser
$ npm publish

Assuming your package name is unique, you should be able to see your package at https://npmjs.com/package/<package>. It can also be published to GitHub, so that it can be directly installed.