Event Listeners
error Event Listeners
When an error event is propagated to a node, any registered event listener functions of type error are invoked. The error event listener function takes three parameters and returns a boolean value:
- fn(DOMString message, DOMString url, DOMString lineNumber)
- The function to be dispatched when an error event is propagated to the node that the event listener is attached to.
- Parameters:
- message - the message being reported
- url - absolute URL of the resource (document) in which the error occurred
- lineNumber - in that resource, the line number where the error occurred
- Return value:
event.returnValue = false
if the error has been handled by this function orevent.returnValue = true
if not
mouseover Event Listeners
When a mouseover event is propagated to a node, any registered event listener functions of type mouseover are invoked. The mouseover event listener function takes one parameter and returns a boolean value:
- fn(Event event)
- The function to be dispatched when a mouseover event is propagated to the node that the event listener is attached to.
- Parameters:
- event - the event
- Return value:
event.returnValue = true
if the event is to be cancelled orevent.returnValue = false
if not
Note that the return value for mouseover event listeners is the opposite from the return value for other event listeners (below).
beforeunload Event Listeners
When a beforeunload event is propagated to a node, any registered event listener functions of type beforeunload are invoked. the beforeunload event listener takes one parameter and returns a string value:
- fn(Event event)
- The function to be dispatched when a beforeunload event is propagated to the node that the event listener is attached to.
- Parameters:
- event - the event
- Return value:
event.returnValue = "Prompt text"
to display a prompt for the user to confirm leaving the page orevent.returnValue = ""
if not
Other Event Listeners
When any other event is propagated to a node, any registered event listener functions of the matching type are invoked. The event listener function takes one parameter and returns a boolean value:
- fn(Event event)
- The function to be dispatched when an event is propagated to the node that the event listener is attached to.
- Parameters:
- event - the event
- Return value:
event.returnValue = false
if the event is to be cancelled orevent.returnValue = true
if not