Event emitter component.
$ component install component/emitter
Register an event
handler fn
.
Register a single-shot event
handler fn
,
removed immediately after it is invoked the
first time.
Remove event
handler fn
, or pass only the event
name to remove all handlers for event
.
Emit an event
with variable option args.
Return an array of callbacks, or an empty array.
Check if this emitter has event
handlers.