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:
listener
{Function}callbacks
{Object}storage
{Value}
Returns a constructed AsyncListener
object. Which can then be passed to
process.addAsyncListener()
and process.removeAsyncListener()
. Each
function parameter is as follows:
listener(storage)
: AFunction
called as an asynchronous event is queued. If a {Value} is returned then it will be attached to the event asstorage
and overwrite any pre-defined value passed tocreateAsyncListener()
. If astorage
argument is passed initially then it will also be passed tolistener()
.callbacks
: AnObject
which may contain three optional fields:before(context, storage)
: AFunction
that is called immediately before the asynchronous callback is about to run. It will be passed both thecontext
(i.e.this
) of the calling function and thestorage
either returned fromlistener
or passed during construction (if either was done).after(context, storage)
: AFunction
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(storage, error)
: AFunction
called if the event's callback threw. Iferror
returnstrue
then Node will assume the error has been properly handled and resume execution normally.
storage
: AValue
(i.e. anything) that will be, by default, attached to all new event instances. This will be overwritten if aValue
is returned bylistener()
.
Returns a constructed AsyncListener
object and immediately adds it to
the listening queue.
Removes the asyncListener
from the listening queue.