1  # inflight
 2  
 3  Add callbacks to requests in flight to avoid async duplication
 4  
 5  ## USAGE
 6  
 7  ```javascript
 8  var inflight = require('inflight')
 9  
10  // some request that does some stuff
11  function req(key, callback) {
12    // key is any random string.  like a url or filename or whatever.
13    //
14    // will return either a falsey value, indicating that the
15    // request for this key is already in flight, or a new callback
16    // which when called will call all callbacks passed to inflightk
17    // with the same key
18    callback = inflight(key, callback)
19  
20    // If we got a falsey value back, then there's already a req going
21    if (!callback) return
22  
23    // this is where you'd fetch the url or whatever
24    // callback is also once()-ified, so it can safely be assigned
25    // to multiple events etc.  First call wins.
26    setTimeout(function() {
27      callback(null, key)
28    }, 100)
29  }
30  
31  // only assigns a single setTimeout
32  // when it dings, all cbs get called
33  req('foo', cb1)
34  req('foo', cb2)
35  req('foo', cb3)
36  req('foo', cb4)
37  ```