emitter-listener

Add dynamic instrumentation to emitters

shimmer does a bunch of the work necessary to wrap other methods in
a wrapper you provide:

``javascript
var EventEmitter = require('events').EventEmitter;
var wrapEmitter = require('emitter-listener');

var ee = new EventEmitter();

var id = 0;

wrapEmitter(
ee,
function mark(listener) {
listener.id = id++;
},
function prepare(listener) {
console.log('listener id is %d', listener.id);
}
);
`

$3

There are times when it's necessary to monkeypatch default behavior in
JavaScript and Node. However, changing the behavior of the runtime on the fly
is rarely a good idea, and you should be using this module because you need to,
not because it seems like fun.

#### wrapEmitter(emitter, mark, prepare)

Wrap an EventEmitter's event listeners. Each listener will be passed to
mark when it is registered with .addListener() or .on(), and then
each listener is passed to prepare to be wrapped before it's called
by the .emit() call. wrapListener deals with the single listener
vs array of listeners logic, and also ensures that edge cases like
.removeListener() being called from within an .emit()` for the same
event type is handled properly.

The wrapped EE can be restored to its pristine state by using
emitter.__unwrap(), but this should only be used if you really know
what you're doing.