Node.js - npm (Node Package Manager)

Node Package Manager (npm) provides following two main functionalities:

• Online repositories for node.js packages/modules which are searchable on search.nodejs.org
• Command line utility to install Node.js packages, do version management and dependency management of Node.js packages.

npm comes bundled with Node.js installables after v0.6.3 version. To verify the same, open console and type following command and see the result:

                               $ npm --version
                               2.7.1

If you are running old version of npm then its damn easy to update it to the latest version. Just use the following command from root:

                               $ sudo npm install npm -g
                               /usr/bin/npm -> /usr/lib/node_modules/npm/bin/npm-cli.js
                               npm@2.7.1 /usr/lib/node_modules/npm

Installing Modules using npm

There is a simple syntax to install any Node.js module:

                                $ npm install <Module Name>

For example, 

following is the command to install a famous Node.js web framework module called express: 

                                $ npm install express

Now you can use this module in your js file as following:

                                var express = require('express')

Global vs Local installation

By default, npm installs any dependency in the local mode. Here local mode refers to the package installation in node_modules directory lying in the folder where Node application is present. Locally deployed packages are accessible via require() method. For example when we installed express module, it created node_modules directory in the current directory where it installed express module.

                                $ ls -l
                                total 0
                                drwxr-xr-x 3 root root 20 Mar 17 02:23 node_modules

Alternatively you can use npm ls command to list down all the locally installed modules.
Globally installed packages/dependencies are stored in system directory. Such dependencies can be used in CLI (Command Line Interface) function of any node.js but can not be imported using require() in Node application directly. Now Let's try installing express module using global installation.

                                 $ npm install express -g

This will produce similar result but module will be installed globally. Here first line tells about the module version and its location where it is getting installed.

express@4.12.2 /usr/lib/node_modules/express
├── merge-descriptors@1.0.0
├── utils-merge@1.0.0
├── cookie-signature@1.0.6
├── methods@1.1.1
├── fresh@0.2.4
├── cookie@0.1.2
├── escape-html@1.0.1
├── range-parser@1.0.2
├── content-type@1.0.1
├── finalhandler@0.3.3
├── vary@1.0.0
├── parseurl@1.3.0
├── content-disposition@0.5.0
├── path-to-regexp@0.1.3
├── depd@1.0.0
├── qs@2.3.3
├── on-finished@2.2.0 (ee-first@1.1.0)
├── etag@1.5.1 (crc@3.2.1)
├── debug@2.1.3 (ms@0.7.0)
├── proxy-addr@1.0.7 (forwarded@0.1.0, ipaddr.js@0.1.9)
├── send@0.12.1 (destroy@1.0.3, ms@0.7.0, mime@1.3.4)
├── serve-static@1.9.2 (send@0.12.2)
├── accepts@1.2.5 (negotiator@0.5.1, mime-types@2.0.10)
└── type-is@1.6.1 (media-typer@0.3.0, mime-types@2.0.10)

You can use following command to check all the modules installed globally:

                                   $ npm ls -g

Using package.json

package.json is present in the root directory of any Node application/module and is used to define the properties of a package. Let's open package.json of express package present in node_modules/express/

{
  "name": "express",
  "description": "Fast, unopinionated, minimalist web framework",
  "version": "4.11.2",
  "author": {
    "name": "TJ Holowaychuk",
    "email": "tj@vision-media.ca"
  },
  "contributors": [
    {
      "name": "Aaron Heckmann",
      "email": "aaron.heckmann+github@gmail.com"
    },
    {
      "name": "Ciaran Jessup",
      "email": "ciaranj@gmail.com"
    },
    {
      "name": "Douglas Christopher Wilson",
      "email": "doug@somethingdoug.com"
    },
    {
      "name": "Guillermo Rauch",
      "email": "rauchg@gmail.com"
    },
    {
      "name": "Jonathan Ong",
      "email": "me@jongleberry.com"
    },
    {
      "name": "Roman Shtylman",
      "email": "shtylman+expressjs@gmail.com"
    },
    {
      "name": "Young Jae Sim",
      "email": "hanul@hanul.me"
    }
  ],
  "license": "MIT",
  "repository": {
    "type": "git",
    "url": "https://github.com/strongloop/express"
  },
  "homepage": "http://expressjs.com/",
  "keywords": [
    "express",
    "framework",
    "sinatra",
    "web",
    "rest",
    "restful",
    "router",
    "app",
    "api"
  ],
  "dependencies": {
    "accepts": "~1.2.3",
    "content-disposition": "0.5.0",
    "cookie-signature": "1.0.5",
    "debug": "~2.1.1",
    "depd": "~1.0.0",
    "escape-html": "1.0.1",
    "etag": "~1.5.1",
    "finalhandler": "0.3.3",
    "fresh": "0.2.4",
    "media-typer": "0.3.0",
    "methods": "~1.1.1",
    "on-finished": "~2.2.0",
    "parseurl": "~1.3.0",
    "path-to-regexp": "0.1.3",
    "proxy-addr": "~1.0.6",
    "qs": "2.3.3",
    "range-parser": "~1.0.2",
    "send": "0.11.1",
    "serve-static": "~1.8.1",
    "type-is": "~1.5.6",
    "vary": "~1.0.0",
    "cookie": "0.1.2",
    "merge-descriptors": "0.0.2",
    "utils-merge": "1.0.0"
  },
  "devDependencies": {
    "after": "0.8.1",
    "ejs": "2.1.4",
    "istanbul": "0.3.5",
    "marked": "0.3.3",
    "mocha": "~2.1.0",
    "should": "~4.6.2",
    "supertest": "~0.15.0",
    "hjs": "~0.0.6",
    "body-parser": "~1.11.0",
    "connect-redis": "~2.2.0",
    "cookie-parser": "~1.3.3",
    "express-session": "~1.10.2",
    "jade": "~1.9.1",
    "method-override": "~2.3.1",
    "morgan": "~1.5.1",
    "multiparty": "~4.1.1",
    "vhost": "~3.0.0"
  },
  "engines": {
    "node": ">= 0.10.0"
  },
  "files": [
    "LICENSE",
    "History.md",
    "Readme.md",
    "index.js",
    "lib/"
  ],
  "scripts": {
    "test": "mocha --require test/support/env --reporter spec --bail --check-leaks test/ test/acceptance/",
    "test-cov": "istanbul cover node_modules/mocha/bin/_mocha -- --require test/support/env --reporter dot --check-leaks test/ test/acceptance/",
    "test-tap": "mocha --require test/support/env --reporter tap --check-leaks test/ test/acceptance/",
    "test-travis": "istanbul cover node_modules/mocha/bin/_mocha --report lcovonly -- --require test/support/env --reporter spec --check-leaks test/ test/acceptance/"
  },
  "gitHead": "63ab25579bda70b4927a179b580a9c580b6c7ada",
  "bugs": {
    "url": "https://github.com/strongloop/express/issues"
  },
  "_id": "express@4.11.2",
  "_shasum": "8df3d5a9ac848585f00a0777601823faecd3b148",
  "_from": "express@*",
  "_npmVersion": "1.4.28",
  "_npmUser": {
    "name": "dougwilson",
    "email": "doug@somethingdoug.com"
  },
  "maintainers": [
    {
      "name": "tjholowaychuk",
      "email": "tj@vision-media.ca"
    },
    {
      "name": "jongleberry",
      "email": "jonathanrichardong@gmail.com"
    },
    {
      "name": "shtylman",
      "email": "shtylman@gmail.com"
    },
    {
      "name": "dougwilson",
      "email": "doug@somethingdoug.com"
    },
    {
      "name": "aredridel",
      "email": "aredridel@nbtsc.org"
    },
    {
      "name": "strongloop",
      "email": "callback@strongloop.com"
    },
    {
      "name": "rfeng",
      "email": "enjoyjava@gmail.com"
    }
  ],
  "dist": {
    "shasum": "8df3d5a9ac848585f00a0777601823faecd3b148",
    "tarball": "http://registry.npmjs.org/express/-/express-4.11.2.tgz"
  },
  "directories": {},
  "_resolved": "https://registry.npmjs.org/express/-/express-4.11.2.tgz",
  "readme": "ERROR: No README data found!"
}

Uninstalling a module

Use following command to uninstall a Node.js module.

                             $ npm uninstall express

Once npm uninstall the package, you can verify by looking at the content
 of /node_modules/ directory or type the following command: 

                             $ npm ls

Updating a module

Update package.json and change the version of the dependency which to be updated and run the following command.

                            $ npm update express

Search a module

Search package name using npm.

                           $ npm search express

Create a module

Creation of module requires package.json to be generated. Let's generate package.json using npm, which will generate basic skeleton of the package.json.

                           $ npm init

This utility will walk you through creating a package.json file.
It only covers the most common items, and tries to guess sane defaults.

See 'npm help json' for definitive documentation on these fields
and exactly what they do.

Use 'npm install <pkg> --save' afterwards to install a package and
save it as a dependency in the package.json file.

Press ^C at any time to quit.
name: (webmaster)

You will need to provide all the required information about your module. YOu can take help from the above mentioned package.json file to understand the meanings of various information demanded. Once package.json is generated. Use the following command to register yourself with npm repository site using a valid email address.

                         $ npm adduser
                         Username: nodeuser
                         Password:
                         Email: (this IS public) nodeuser@gmail.com

Now its time to publish your module:

                         $ npm publish

If everything is fine with your module, then it will be published in the reporsitory and will be accessible to install using npm like any other other Node.js module.