# require-in-the-middle

Hook into the Node.js `require` function. This allows you to modify
modules on-the-fly as they are being required.

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## Installation

```
npm install require-in-the-middle --save
```

## Usage

```js
const path = require('path')
const Hook = require('require-in-the-middle')

// Hook into the express and mongodb module
Hook(['express', 'mongodb'], function (exports, name, basedir) {
  const version = require(path.join(basedir, 'package.json')).version

  console.log('loading %s@%s', name, version)

  // expose the module version as a property on its exports object
  exports._version = version

  // whatever you return will be returned by `require`
  return exports
})
```

## API

The require-in-the-middle module exposes a single function:

### `hook = Hook([modules][, options], onrequire)`

When called a `hook` object is returned.

Arguments:

- `modules` <string[]> An optional array of module names to limit which modules
  trigger a call of the `onrequire` callback. If specified, this must be the
  first argument. Both regular modules (e.g. `react-dom`) and
  sub-modules (e.g. `react-dom/server`) can be specified in the array.
- `options` <Object> An optional object containing fields that change when the
  `onrequire` callback is called. If specified, this must be the second
  argument.
  - `options.internals` <boolean> Specifies whether `onrequire` should be called
    when module-internal files are loaded; defaults to `false`.
- `onrequire` <Function> The function to call when a module is required.

The `onrequire` callback will be called the first time a module is
required. The function is called with three arguments:

- `exports` <Object> The value of the `module.exports` property that would
  normally be exposed by the required module.
- `name` <string> The name of the module being required. If `options.internals`
  was set to `true`, the path of module-internal files that are loaded
  (relative to `basedir`) will be appended to the module name, separated by
  `path.sep`.
- `basedir` <string> The directory where the module is located, or `undefined`
  for core modules.

Return the value you want the module to expose (normally the `exports`
argument).

### `hook.unhook()`

Removes the `onrequire` callback so that it will not be triggerd by
subsequent calls to `require()`.

## License

[MIT](https://github.com/elastic/require-in-the-middle/blob/master/LICENSE)