async-listener

This is an implementation of Trevor Norris's process.{addAsyncListener,removeAsyncListener} API for adding behavior to async calls. You can see his implementation (currently a work in progress) on Node.js core pull request #6011. This polyfill / shim is intended for use in versions of Node prior to whatever version of Node in which Trevor's changes finally land (anticipated at the time of this writing as 0.11.7).
Here's his documentation of the intended API, which will probably get cleaned up here later:

createAsyncListener(callbacks, initialStorage)

• callbacks {Object}
• initialStorage {Value}

Returns a constructed AsyncListener object. Which can then be passed to process.addAsyncListener() and process.removeAsyncListener(). Each function parameter is as follows:

1. callbacks: An Object which may contain four optional fields:

* `create`: A `function (storage)` that is called when an asynchronous event
  is queued. Recives the `storage` attached to the listener. `storage` can be
  created by passing an `initialStorage` argument during construction, or by
  returning a `Value` from `create` which will be attached to the listener
  and overwrite the `initialStorage`.
* `before`: A `function (context, storage)` that is called immediately
  before the asynchronous callback is about to run. It will be passed both
  the `context` (i.e. `this`) of the calling function and the `storage`.
* `after`: A `function (context, storage)` called immediately after the
  asynchronous event's callback is run. Note that if the event's callback
  throws during execution this will not be called.
* `error`: A `function (storage, error)` called if the event's callback
  threw. If `error` returns `true` then Node will assume the error has been
  properly handled and resume execution normally.

1. initialStorage: A Value (i.e. anything) that will be, by default,

attached to all new event instances. This will be overwritten if a `Value`
is returned by `create()`.

addAsyncListener(callbacks, initialStorage)

addAsyncListener(asyncListener)

Returns a constructed AsyncListener object and immediately adds it to the listening queue.

removeAsyncListener(asyncListener)

Removes the asyncListener from the listening queue.