## Managing dependencies

Ok, so you've built your first module, but now you want to make it use one of the many libraries available via the npm registry.


### finding modules

There are a few ways to find a module.  You can use http://npmjs.org or http://npmsearch.com to find modules that may fit what you need.

#### some advice for choosing modules

```
Modules should have tests, and they should try to only export a single function
```

You'll develop more criteria as you start digging through more modules, don't be afraid to read their source!

### installing modules

So you've found a module that you want to install, we'll use the `request` module to demonstrate how to make it a dependency of `your-first-node-module`

```bash
cd your-first-node-module
npm install --save request
```

Ok, that should have dumped a bunch of text to your terminal.  NPM does a bunch of work to make sure it gets all of the dependencies (recursively!) of the module you are installing

the `--save` flag will update your package.json with the version of `request` installed

```
$ cat package.json
{
  "name": "your-first-node-module",
  "version": "1.0.0",
  "description": "very first module",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Elijah Insua <tmpvar@gmail.com> (http://tmpvar.com)",
  "license": "MIT",
  "dependencies": {
    "request": "~2.33.0"
  }
}
```

#### what does my dependency tree look like?

```
$ npm list
your-first-node-module@1.0.0 /Users/tmpvar/work/tmp/your-first-node-module
└─┬ request@2.33.0
  ├── aws-sign2@0.5.0
  ├── forever-agent@0.5.0
  ├─┬ form-data@0.1.2
  │ ├── async@0.2.10
  │ └─┬ combined-stream@0.0.4
  │   └── delayed-stream@0.0.5
  ├─┬ hawk@1.0.0
  │ ├── boom@0.4.2
  │ ├── cryptiles@0.2.2
  │ ├── hoek@0.9.1
  │ └── sntp@0.2.4
  ├─┬ http-signature@0.10.0
  │ ├── asn1@0.1.11
  │ ├── assert-plus@0.1.2
  │ └── ctype@0.5.2
  ├── json-stringify-safe@5.0.0
  ├── mime@1.2.11
  ├── node-uuid@1.4.1
  ├── oauth-sign@0.3.0
  ├── qs@0.6.6
  ├─┬ tough-cookie@0.12.1
  │ └── punycode@1.2.3
  └── tunnel-agent@0.3.0
```

### Ok, thats great.. how do I use request?

We'll demonstrate that by using it in the repl

```
$ cd your-first-node-module
$ node
> var request = require('request')
undefined
> request.get('http://google.com/', function(error, response, body) { console.log(body); })
... whole bunch of data ...
.. pause ..
.. a bunch of html ..
```

And that's how you use a node module installed from npm


#### installing development time modules

if you need modules to support your tests or local development you can `npm install --save-dev` and they will be placed in your `devDependencies` section of your project's `package.json`.

__note__: these modules will only be installed when you `npm install` from inside of your project.  Users of your project will not need to install the development dependencies and npm will ignore them when installing your module as a dependency