This method allows the registration of event listeners on the event target.
If an EventListener is added to an EventTarget while it is processing an
event, it will not be triggered by the current actions but may be
triggered during a later stage of event flow, such as the bubbling phase.
If multiple identical EventListeners are registered on the same
EventTarget with the same parameters the duplicate instances are
discarded. They do not cause the EventListener to be called twice
and since they are discarded they do not need to be removed with the
removeEventListener method.
| type | The event type for which the user is registering |
| listener | The listener parameter takes an interface implemented by the user which contains the methods to be called when the event occurs. |
| useCapture | If true, useCapture indicates that the user wishes to initiate capture. After initiating capture, all events of the specified type will be dispatched to the registered EventListener before being dispatched to any EventTargets beneath them in the tree. Events which are bubbling upward through the tree will not trigger an EventListener designated to use capture. |
| wantsUntrusted | If false, the listener will not receive any untrusted events (see above), if true, the listener will receive events whether or not they're trusted |
addSystemEventListener() adds an event listener of aType to the system
group. Typically, core code should use system group for listening to
content (i.e., non-chrome) element’s events. If core code uses
nsIDOMEventTarget::AddEventListener for a content node, it means
that the listener cannot listen the event when web content calls
stopPropagation() of the event.
| aType | An event name you're going to handle. |
| aListener | An event listener. |
| aUseCapture | TRUE if you want to listen the event in capturing phase. Otherwise, FALSE. |
| aWantsUntrusted | TRUE if you want to handle untrusted events. Otherwise, FALSE. |
| NS_OK if succeed. Otherwise, NS_ERROR_*. |
This method allows the removal of event listeners from the event
target. If an EventListener is removed from an EventTarget while it
is processing an event, it will not be triggered by the current actions.
EventListeners can never be invoked after being removed.
Calling removeEventListener with arguments which do not identify any
currently registered EventListener on the EventTarget has no effect.
| type | Specifies the event type of the EventListener being removed. |
| listener | The EventListener parameter indicates the EventListener to be removed. |
| useCapture | Specifies whether the EventListener being removed was registered as a capturing listener or not. If a listener was registered twice, one with capture and one without, each must be removed separately. Removal of a capturing listener does not affect a non-capturing version of the same listener, and vice versa. |
removeSystemEventListener() should be used if you have used
addSystemEventListener().
This method allows the dispatch of events into the implementations
event model. Events dispatched in this manner will have the same
capturing and bubbling behavior as events dispatched directly by the
implementation. The target of the event is the EventTarget on which
dispatchEvent is called.
| evt | Specifies the event type, behavior, and contextual information to be used in processing the event. |
| Indicates whether any of the listeners which handled the event called preventDefault. If preventDefault was called the value is false, else the value is true. @throws INVALID_STATE_ERR: Raised if the Event's type was not specified by initializing the event before dispatchEvent was called. Specification of the Event's type as null or an empty string will also trigger this exception. |
Returns the nsIDOMEventTarget object which should be used as the target
of DOMEvents.
Usually |this| is returned, but for example global object returns
the outer object.
Returns the nsIDOMEventTarget object which should be used as the target
of the event and when constructing event target chain.
Usually |this| is returned, but for example global object returns
the inner object.
Called before the capture phase of the event flow.
This is used to create the event target chain and implementations
should set the necessary members of EventChainPreVisitor.
At least aVisitor.mCanHandle must be set,
usually also aVisitor.mParentTarget if mCanHandle is PR_TRUE.
First one tells that this object can handle the aVisitor.mEvent event and
the latter one is the possible parent object for the event target chain.
@see EventDispatcher.h for more documentation about aVisitor.
@note Only EventDispatcher should call this method.
| aVisitor | the visitor object which is used to create the event target chain for event dispatching. |
If EventChainPreVisitor.mWantsWillHandleEvent is set PR_TRUE,
called just before possible event handlers on this object will be called.
Called after the bubble phase of the system event group.
The default handling of the event should happen here.
@see EventDispatcher.h for documentation about aVisitor.
@note Only EventDispatcher should call this method.
| aVisitor | the visitor object which is used during post handling. |
Dispatch an event.
@note If both aEvent and aDOMEvent are used, aEvent must be the internal
event of the aDOMEvent.
If aDOMEvent is not nullptr (in which case aEvent can be nullptr) it is used
for dispatching, otherwise aEvent is used.
@deprecated This method is here just until all the callers outside Gecko
have been converted to use nsIDOMEventTarget::dispatchEvent.
| aEvent | the event that is being dispatched. |
| aDOMEvent | the event that is being dispatched, use if you want to dispatch nsIDOMEvent, not only WidgetEvent. |
| aPresContext | the current presentation context, can be nullptr. |
| aEventStatus | the status returned from the function, can be nullptr. |
Get the script context in which the event handlers should be run.
May return null.
@note Caller must check the value of aRv.
If the method above returns null, but a success code, this method
is called.