Event

♪ What a wonderful mess (it would be) ♫

Event management is one of the really sore spots of cross-browser scripting.

True, the prominent issue is: everybody does it the W3C way, and MSIE does it another way altogether. But there are quite a few subtler, sneakier issues here and there waiting to bite your ankle, such as the keypress/keydown issue with KHTML-based browsers (Konqueror and Safari). Also, MSIE has a tendency to leak memory when it comes to discarding event handlers.

Prototype to the rescue!

Of course, Prototype smooths it over so well you’ll forget these troubles even exist. Enter the Event namespace. It is replete with methods (listed at the top and bottom of this page), that all take the current event object as an argument, and happily produce the information you’re requesting, across all major browsers.

Event also provides a standardized list of key codes you can use with keyboard-related events. The following constants are defined in the namespace: KEY_BACKSPACE, KEY_TAB, KEY_RETURN, KEY_ESC, KEY_LEFT, KEY_UP, KEY_RIGHT, KEY_DOWN, KEY_DELETE, KEY_HOME, KEY_END, KEY_PAGEUP, KEY_PAGEDOWN. The names are self-explanatory.

The functions you’re most likely to use a lot are observe, element and stop. As for the others, your mileage may vary; it’s all about what your web app does.

Instance methods on event objects
1.6

As of Prototype 1.6, all methods on the Event object are now also available as instance methods on the event object itself:

Before

$('foo').observe('click', respondToClick);

function respondToClick(event) {
  var element = Event.element(event);
  element.addClassName('active');
}

After

$('foo').observe('click', respondToClick);

function respondToClick(event) {
  var element = event.element();
  element.addClassName('active');
}

These methods are added to the event object through Event.extend, in the same way that Element methods are added to DOM nodes through Element.extend. Events are extended automatically when handlers are registered with Prototype’s Event.observe method; if you’re using a different method of event registration, for whatever reason, you’ll need to extend these events manually with Event.extend.

Methods

element

Event.element(event) -> Element

Returns the DOM element on which the event occurred.

extend
1.6

Event.extend(event)

Extends event with all of the methods contained in Event.Methods.

findElement

Event.findElement(event, tagName) -> Element

Returns the first DOM element with a given tag name, upwards from the one on which the event occurred.

isLeftClick

Event.isLeftClick(event) -> Boolean

Determines whether a button-related mouse event was about the “left” (primary, actually) button.

observe

Event.observe(element, eventName, handler[, useCapture = false])

Registers an event handler on a DOM element.

pointerX

Event.pointerX(event) -> Number

Returns the absolute horizontal position for a mouse event.

pointerY

Event.pointerY(event) -> Number

Returns the absolute vertical position for a mouse event.

stop

Event.stop(event)

Stops the event’s propagation and prevents its default action from being triggered eventually.

stopObserving

Event.stopObserving(element, eventName, handler[, useCapture = false])

Unregisters an event handler.

unloadCache
1.6

Event.unloadCache()

Unregisters all event handlers registered through observe. Automatically wired for you. Not available since 1.6.