parent-require/README.md

Require modules from parent modules.

# parent-require

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Require modules from parent (i.e. loading) module.

## Install

    $ npm install parent-require

## Usage

`parent-require` addresses an annoying error condition that arises when
developing plugins, which have [peer dependencies](http://blog.nodejs.org/2013/02/07/peer-dependencies/),
that are `npm link`'d into an application.

The problem is best illustrated by example.  We'll use a shared package of [Mongoose](http://mongoosejs.com/)
schemas, but the concept applies equally well to any module you plugin to a
larger framework.

#### Develop a Plugin for a Framework

Let's develop a set of shared [Mongoose](http://mongoosejs.com/) schemas for a
user database, packaged as `mongoose-schemas-users` for reuse by any application
that needs to query the database.

```javascript
var mongoose = require('mongoose');

var UserSchema = new mongoose.Schema(...);

module.exports = UserSchema;
```

The important bit here is that `mongoose` is a *peer dependency* of this
package.

#### Require a Plugin from an App

Now, let's install this package...

    npm install mongoose-schemas-users

..and require it within our application:

```javascript
var mongoose = require('mongoose')
  , schemas = require('mongoose-schemas-users')
  
mongoose.model('User', schemas.UserSchema);
```

So far, so good.

#### npm link Plugin for Development

During the course of developing the application, we discover that we need to
tweak the schemas we've defined.  This is usually easy:

    npm link mongoose-schemas-users

We've made some edits, and run the application:

    Error: Cannot find module 'mongoose'

WTF?!?  This issue arises because `mongoose` is a *peer dependency*.  Now that
it has been `npm link`'d to a directory that resides outside of the application
itself, Node's typical resolution algorithm fails to find it.

#### Fallback to Parent Require

This is where `parent-require` comes into play.  It provides a fallback to
`require` modules from the *loading* (aka parent) module.  Because the loading
module exists within the application itself, Node's resolution algorithm will
correctly find our peer dependency.

```javascript
try {
  var mongoose = require('mongoose');
} catch (_) {
  // workaround when `npm link`'ed for development
  var prequire = require('parent-require')
    , mongoose = prequire('mongoose');
}

var UserSchema = new mongoose.Schema(...);

module.exports = UserSchema;
```

With the fallback in place, we can both `npm install` and `npm link` this
plugin, correctly resolving peer dependencies in both cases.

## Tests

    $ npm install
    $ npm test

## Credits

  - [Jared Hanson](http://github.com/jaredhanson)

## License

[The MIT License](http://opensource.org/licenses/MIT)

Copyright (c) 2013 Jared Hanson <[http://jaredhanson.net/](http://jaredhanson.net/)>