inflight

Add callbacks to requests in flight to avoid async duplication

USAGE

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