EventEmitter.once

This method adds a listener that is removed automatically after it has been called.

Usage

emitter.once(event, listener, dependencies)

Arguments

Argument	Type	Required	Description
event	string	✓	The name of the event.
listener	function	✓	The listener function added for that event.
dependencies	array or array-like object of functions		List of dependencies for that listener.

Return

The this EventEmitter instance.

Exceptions

• Throws a TypeError when listener is not a function.
• Throws a TypeError when dependencies is array or array-like objects, but contain other than function.
• Throws a ReferenceError when dependencies contain the listener (e.g. attempt to make listener dependency of itself).

Remarks

If a dependency is not added for as a listener for the given event, it'll be added as long as there are dependent listeners for it.

If listener already added for the specified event, following operation might happen:

• If a listener is added as dependency by some early call, it'll be promoted to once listener. If listener is normal listener, it'll remain a normal listener.
• If a list of dependencies is specified, it'll merged with current dependencies.

TODO

In case once called with listener that is already added as a normal listener, dependencies specified by once should be removed after the first call.