04 - Installing npm packages locally

Installing npm packages locally

There are two ways to install npm packages: locally or globally. You choose which kind of installation to use based on how you want to use the package.

If you want to depend on the package from your own module using something like Node.js' require, then you want to install locally, which is npm install's default behavior. On the other hand, if you want to use it as a command line tool, something like the grunt CLI, then you want to install it globally.

To learn more about the install command's behavior, check out the CLI doc page.

Installing

A package can be downloaded with the command

> npm install <package_name>

This will create the node_modules directory in your current directory(if one doesn't exist yet), and will download the package to that directory.

Test:

To confirm that npm install worked correctly, check to see that a node_modules directory exists and that it contains a directory for the package(s) you installed. You can do this by running ls node_modules on Unix systems, e.g. "OSX", "Debian", or dir node_modules on Windows.

Example:

Install a package called lodash. Confirm that it ran successfully by listing the contents of the node_modules directory and seeing a directory called lodash.

> npm install lodash
> ls node_modules               # use `dir` for Windows
 
#=> lodash

Which version of the package is installed?

If there is no package.json file in the local directory, the latest version of the package is installed.

If there is package.json file, the latest version satisfying the semver rule declared in package.json for that package (if there is any) is installed.

Using the installed package

Once the package is in node_modules, you can use it in your code. For example, if you are creating a Node.js module, you can require it.

Example:

Create a file named index.js, with the following code:

// index.js 
var lodash = require('lodash');
 
var output = lodash.without([1, 2, 3], 1);
console.log(output);

Run the code using node index.js. It should output [2, 3].

If you had not properly installed lodash, you would receive this error:

module.js:340
    throw err;
          ^
Error: Cannot find module 'lodash'

To fix this, run npm install lodash in the same directory as your index.js.