mySelection.on( eventName, eventHandler, capturePhase ) in D3.js

Retrieve the event listener for an event type.

Arguments

name	type	description
eventName	String	Name of the event, e.g. ‘click’ or ‘mouseover’. To register multiple handlers for the same type on the same element, use a trailing namespace, e.g. ‘click.foo’ and ‘click.bar’.
eventHandler	Function	Function to be invoked when the event occurs. Will be passed the datum for the current object, the index of that object in the selection, and with the `this` context set to the DOM element. To remove an event handler, pass `null` for this parameter.
capturePhase	Boolean	Corresponds to the W3C useCapture flag.