Interesting findings (mostly related to IE):

This test tries to define if the HTML event handlers (onFoo) are linked to the 
add/removeEventListener APIs in any way (or to define what the relationship is).

Browsers tested: Opera 9.25, Firefox 3 RC1, IE8 Beta1, Safari 3.1.1.

(on IE, I substituted attach/detachEvent for add/removeEventListener)

The findings appear to indicate that:

1.  All tested browsers follow a basic model in that an HTML event handler is 
maintained separately (perhaps in a separate queue) from event handlers 
attached via programmatic means (e.g., addEventListener/attachEvent). This can 
be verified by adding an HTML event handler and then trying to delete the 
reference to its DOM attribute via removeEventListener.

In addition to this basic conclusion, there were a few discrepencies in event 
handling that should be noted:

* IE/Firefox/Opera all keep a reference alive to the HTML event handler via the 
element's 'onclick' DOM attribute even after the content attribute has been 
* Safari also keeps a reference to the element's 'onclick' handler, yet the 
"body" of the handler may be missing if the element's content attribute is 
removed (this prevents adding an event listener via the DOM attribute if the 
content attribute is missing).
* IE's attachEvent is cumulative, despite re-applying the same handler over and 
over. detachEvent works in reverse, removing references until none are left.
* IE has a bug that HTML event handlers are not actually removed via 
removeAttribute (though the attribute itself is removed). This is being fixed 
in IE8, but does impact this test page :(

Title: onFoo versus programmatic event handlers

onFoo versus add/removeEventListener(foo)

This test checks the relationship between HTML inline event handlers and programmatically-added event handlers for both the Microsoft and W3C event handling models.

The box below is the testing area for mouse events. It has no events attached by default when the page loads. The buttons below the box control the adding/removing of the following event handler to the box:

  • onclick - cycle the color of the box from (0)red -> (1)orange -> (2)yellow -> (3)green -> (4)blue

The buttons below it control the dynamic addition/removal of the event via the various dynamic mechanisms supported by browsers.

Event handler manipulation via the Element  
Event handler manipulation via the EventTarget Handler Attached: no
Event handler manipulation via the EventTarget with references to the Element's DOM property Handler Attached: no

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