[whatwg] Overriding functions in DOM Storage

Ian Hickson ian at hixie.ch
Thu Jun 11 11:52:23 PDT 2009

On Fri, 22 May 2009, Jeremy Orlow wrote:
> What is the behavior of the following supposed to be?
> window.sessionStorage.removeItem = function(x) { alert("Wait, this works?"); };
> window.sessionStorage.removeItem('blah');
> alert(typeof window.sessionStorage.removeItem);

The behaviour of these things are defined in WebIDL:


...which, as defined today, consists of setting 'removeItem' to a function 
value that doesn't persist.

> Safari shows 2 alerts, and the second one says 'function'.

This appears to be correct according to WebIDL today.

> If Safari's implementation is correct (and it's good for the implementations
> to be overridable), then I believe there needs to be some safe way to make
> .clear() usable again.

On Fri, 22 May 2009, Jeremy Orlow wrote:
> Never mind.  "delete window.localStorage.clear;" should handle this use 
> case.


On Fri, 22 May 2009, Jeremy Orlow wrote:
> The spec would also need to make it clear that removeItem, setItem, etc 
> are special and should not be serialized to disk.

They are serialised to disk if you ever call the actual setter with those 
names; it's just that in this case you never call that setter.

> That said, IE8 doesn't support the delete operator in this fashion and 
> .clear() does not reset functions in Safari 4 (beta).

.clear() indeed would not affect the functions.

On Fri, 22 May 2009, Maciej Stachowiak wrote:
> DOM methods are normally overridable. That would make the Safari 
> behavior correct. If we want the behavior to be different in this case, 
> then the spec should spell that out. Perhaps part of the issue here is 
> that the definition of the [NameSetter] extended attribute in Web IDL 
> doesn't make clear whether or not name setter behavior takes precedence 
> over setting existing predefined attributes or methods.

It seems clear to me.

On Tue, 26 May 2009, Jeremy Orlow wrote:
> What's special here is that everything set with the implicit 
> getters/setters is supposed to be turned into a string.  So yes this 
> does seem somewhat unique.

The special setters aren't invoked in this particular case according to 

> I think it's important to decide which behavior makes the most sense and 
> standardize on it.  The way things are now is pretty useless to eveyone.

Implementors need to make sure they read WedIDL. :-)

On Tue, 26 May 2009, Jeremy Orlow wrote:
> Oh yeah, it's also a bit odd because values persist.  Which doesn't 
> really make sense if we allow functions to be overridden by functions, 
> but does make sense if we're overriding them with strings.

They only persist if the custom setter is invoked.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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