HORIZON PROJECT

# inflight

Add callbacks to requests in flight to avoid async duplication

## USAGE

```javascript

var inflight = require('inflight')

// some request that does some stuff

function req(key, callback) {

  // key is any random string.  like a url or filename or whatever.

  //

  // will return either a falsey value, indicating that the

  // request for this key is already in flight, or a new callback

  // which when called will call all callbacks passed to inflightk

  // with the same key

  callback = inflight(key, callback)

  // If we got a falsey value back, then there's already a req going

  if (!callback) return

  // this is where you'd fetch the url or whatever

  // callback is also once()-ified, so it can safely be assigned

  // to multiple events etc.  First call wins.

  setTimeout(function() {

    callback(null, key)

  }, 100)

}

// only assigns a single setTimeout

// when it dings, all cbs get called

req('foo', cb1)

req('foo', cb2)

req('foo', cb3)

req('foo', cb4)

```