Node.js Tutorial - Node.js NPM

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Node Package Manger, NPM, is a way to share node_modules with the community.

package.json

NPM uses a simple JSON file called package.json to share module information.

To create a package.json file in the current folder, just run the the following code.

$npm init 

This will ask you a few questions such as the name of the module and its version.

Just press enter until the end.

This creates a package.json in the current folder with the name set to the current folder, version set to 0.0.0, and a few other reasonable defaults.

{ 
    "name": "myData", 
    "version": "0.0.0", 
    "description": "", 
    "main": "index.js", 
    "scripts": {
        "test": "echo \"Error: no test specified\" && exit 1" 
    }, 
    "author": "", 
    "license": "ISC" 
} 

Installing an NPM Package

Let's install a module, for example, underscore (www.npmjs.org/package/underscore) to a folder.

To download the latest version of underscore, you simply run the following command.

$ npm install underscore 

The code above generates the following result.

This will download the latest version of underscore from npmjs.org and put it into node_modules/underscore in the current folder.

To load this module, all you need to do now is make a require('underscore') call.

The following code loads the underscore library and outputs the minimum element of an array to the console.

var _ = require('underscore'); 
console.log(_.min([3, 1, 2])); // 1 

The code above generates the following result.

Saving Dependencies

Whenever you run npm install, you have an optional command line flag available --save that tells NPM to write the information about what you installed into package.json.

Do the npm init to create a package file.

$ npm init

Issue the following command to save information to package.json.

$ npm install underscore --save 

The code above generates the following result.

If you run install with ?-save, not only will it download underscore into node_modules, it will also update dependencies inside package.json to point to the installed version of underscore.

"dependencies": { 
    "underscore": "^1.6.0" 
} 

By keeping track of dependencies, we know which published version of a particular library we are using.

Refresh the node_modules Folder

To refresh the node_modules folder from our package.json, we can run the following command:

$ npm install 

This simply looks at your package.json file and downloads a fresh copy of the dependencies specified in your package.json.

Listing All Dependencies

To see which packages you have installed, run npm ls command.

$ npm ls 
...
+-- underscore@1.6.0 

Removing a Dependency

To remove a package, use either the npm uninstall or npm rm command, and specify one or more package names.

npm rm underscore --save deletes the underscore folder from node_modules locally and modifies the dependencies section of your package.json.

You can remove global packages by providing the -g option.

The following code shows how to remove the commander module using npm rm.

package.json Online Dependency Tracking

The following code shows Installing a Module with Lots of Dependencies

$ npm install request 
npm http GET https://registry.npmjs.org/request 
npm http GET https://registry.npmjs.org/tunnel-agent 
npm http GET https://registry.npmjs.org/json-stringify-safe 
...truncated... 
npm http 304 https://registry.npmjs.org/delayed-stream/0.0.5 
request@2.34.0 node_modules\request 
+-- aws-sign2@0.5.0 
...truncated... 
+-- json-stringify-safe@5.0.0 
+-- form-data@0.1.2 (async@0.2.10, combined-stream@0.0.4) 

NPM not only installed request but also brought down a number of other packages that request depends upon.

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