[whatwg] Specification unclear about how HTMLElement.prototype.onscroll's getter/setter should behave for "body" elements

Boris Zbarsky bzbarsky at MIT.EDU
Mon Dec 3 05:58:14 PST 2012

Consider this testcase:

   var desc = Object.getOwnPropertyDescriptor(HTMLElement.prototype,
   desc.set.call(document.body, function() { alert(this); });

Is the listener added on the body, or the window?

The relevant parts of the spec are:

1)  "onscroll" is present on both HTMLElement.prototype and 
HTMLBodyElement.prototype.  This testcase explicitly invokes the setter 
for the former.

2)  The spec text at 
(scroll up; there is no way to link to the actual text) says:

   The following are the event handlers (and their corresponding event
   handler event types) that must be supported by all HTML elements
   other than body and frameset, as both content attributes and IDL
   attributes, and on Document objects, as IDL attributes

It's not clear to me what this means since the properties are on 
HTMLElement.prototype so they can be applied to all HTML elements.  What 
does this text mean in terms of the testcase above?

Basically, I can see three possible behaviors here.  Either the 
HTMLElement.prototype.onscroll setter behaves the same way on all 
elements (and hence the above adds the event handler on the body) or it 
behaves specially for the body element, forwarding to the window (and 
then we don't need HTMLBodyElement.prototype.onscroll), or it throws for 
the body element.  Which one is intended?


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