class method Event.stopObserving

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Event.stopObserving(element[, eventName[, handler]]) → Element
  • element (Element | String) – The element to stop observing, or its ID.
  • eventName (String)(Optional) The name of the event to stop observing, in all lower case, without the "on" — e.g., "click" (not "onclick").
  • handler (Function)(Optional) The handler to remove; must be the exact same reference that was passed to Event.observe.

Unregisters one or more event handlers.

If handler is omitted, unregisters all event handlers on element for that eventName. If eventName is also omitted, unregisters all event handlers on element. (In each case, only affects handlers registered via Prototype.)



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

...we can stop observing using that handler like so:

$('foo').stopObserving('click', myHandler);

If we want to remove all 'click' handlers from 'foo', we leave off the handler argument:


If we want to remove all handlers for all events from 'foo' (perhaps we're about to remove it from the DOM), we simply omit both the handler and the event name:

A Common Error

When using instance methods as observers, it's common to use Function#bind on them, e.g.:

$('foo').observe('click', this.handlerMethod.bind(this));

If you do that, this will not work to unregister the handler:

$('foo').stopObserving('click', this.handlerMethod.bind(this)); // <== WRONG

Function#bind returns a new function every time it's called, and so if you don't retain the reference you used when observing, you can't unhook that function specifically. (You can still unhook all handlers for an event, or all handlers on the element entirely.)

To do this, you need to keep a reference to the bound function:

this.boundHandlerMethod = this.handlerMethod.bind(this);
$('foo').observe('click', this.boundHandlerMethod);

...and then to remove:

$('foo').stopObserving('click', this.boundHandlerMethod); // <== Right