On Apr 18, 2012, at 9:29 AM, Brendan Eich wrote:
> Herby Vojčík wrote:
>> Herby Vojčík wrote:
>>>
>>> Maybe allowing
>>> let {b, b:{x,y}} = obj;
>>> would be enough. It sort-of comforms to existing syntax as well as
>>> semantics.
>>
>> BTW, if you use var instead of let, if already works out of the box (in FF11
>> firebug console; just tried), so why include as if it already is there,
>> albeit in different form?
>
> We implemented destructuring years ago to implementor- and user-test ES4
> proposals. They did not forbid duplicates. That's all.
>
> Nothing normative in experimental Firefox implementation features, of course.
> You cite them as "already [there]" and that's true but it doesn't govern what
> goes into ES6.
But is also works this way according to the ES6 draft spec. It works with var
because var allows duplicated declarations:
var a=1;
var a=2;
var a=3;
which, from a declaration perspective isn't really any different from
var a=1,a=2,a=3;
However let/const does not:
{ //block level duplicate declaration early error
let b=1;
let b=2;
}
or just
let b=1,b=2 ; //block level duplicate declaration error
var {b,b:{x,y}} = obj; //fine because var declaration static semantics don't
disallow duplicates
{ //avoid any conflicts with the preceeding var
let {b,b:{x,y}} = obj; //block level duplicate declaration
}
You might argue that the second b in the destructuring isn't actually
introducing a binding for b. However, syntactically it looks like one and
that is what the static semantic rule is driven off of. If we allow that, we
would also be allowing:
let b=somethingElse;
let {b:{x,y})=obj;
If we want to allow that I'll have to some up with a different way to specify
the static semantics.
Allen
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