[whatwg] [html5] scope chain for event handlers specified via content attributes

Boris Zbarsky bzbarsky at MIT.EDU
Thu Sep 8 18:30:29 PDT 2011

On 9/8/11 8:23 PM, David Flanagan wrote:
> function(event) {
> with(event.target.ownerDocument) {
> with(event.target.form || {}) {
> with(event.target) {
> alert(x);
> }
> }
> }
> }

This is almost exactly how Chrome implements it.  It's all sorts of 
buggy.  See http://code.google.com/p/chromium/issues/detail?id=80911

> But § says that the scope chain should be initialized statically
> when the content attribute string is converted to a function. I'd like
> to check that that is intentional

It's what most UAs implement, I believe... and doesn't suffer from the 
sorts of issues mentioned in the bug report above.

> since it causes counter-intiuitive
> (to me) behavior if an element moves between forms or moves between
> documents after the event handler attribute is set.

So it does.  Of course people should ideally not be using this syntax to 
start with, so it's mostly there for legacy pages that don't often do 
this sort of thing.

> My results: Firefox and Safari create the scope chain statically: when
> an element moves between forms, the scope chain remains the same.
> Chrome's scope chain is dynamic and resolves identifiers against the
> element's new form. Chrome's behavior seems more sensible to me. Is it
> correct?

As implemented, no, in my opinion.  See above.

> (When an element moves from one document to another (via adoptNode())
> firefox uses dynamic scope (perhaps because it is re-creating the
> function?)

What actually happens in this case in Firefox internally is that the 
parent (in the JS_GetParent) sense of the element's JS reflection is 
changed.  This was done because origin determination for JS objects 
depended on the scope chain, since Spidermonkey didn't offer any other 
good way to do it.

With ongoing changes to Spidermonkey, this implementation detail may 
change, and then we may be able to preserve static scope in general, maybe.

In any case, the behavior there is definitely an artifact of 
implementation details, and not intentional.

> In Chrome and Safari, the event handler stops working when
> the element is moved from one document to another, so the test doesn't
> succeed there.)

It's worth testing Opera and various IE versions here too.


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