restrictions on let declarations

John Lenz concavelenz at gmail.com
Thu Jan 30 11:59:56 PST 2014


Yes, that was my point, that is has to be allowed currently and this is a
change.  Using what incorrectly? Existing "const" and "function"
implementations?  Or if "scoped" declarations?


On Thu, Jan 30, 2014 at 11:35 AM, Oliver Hunt <oliver at apple.com> wrote:

>
> On Jan 30, 2014, at 11:27 AM, John Lenz <concavelenz at gmail.com> wrote:
>
> I don't argue that it isn't a useless "let".  I do point out that in
> "sloppy" mode, that other declaration are allow in practices by browsers.
>  Chrome allows function, const, and var in the body of an if without block.
>
>
> That's because they _have_ to be allowed as these constructs are used on
> millions (billions?) of web pages.  Disallowing that behaviour would break
> the web and we can't do that.
>
> Introducing new constructs that expose the same coding problems is not
> worth it - maybe we would want to change something in the future but we
> would already have been burned by existing content using this code
> incorrectly.
>
> --Oliver
>
>
> It does seems like an unnecessary restriction, and with it I'll need to
> make sure that Closure Compiler doesn't introduce these when stripping
> blocks, not a big deal just one more thing to deal with.
>
> I was just hoping that the restriction was enabling something and not just
> noise.
>
>
> On Thu, Jan 30, 2014 at 11:00 AM, Brendan Eich <brendan at mozilla.com>wrote:
>
>> John Barton wrote:
>>
>>>  Not silly. Can you suggest any on-line that most JS developers can
>>> understand discussing how these two forms differ?
>>>
>>> Here are some that describe them as equivalent:
>>>
>>> http://en.wikipedia.org/wiki/JavaScript_syntax#If_..._else
>>> http://msdn.microsoft.com/en-us/library/kw1tezhk(v=vs.94).aspx <
>>> http://msdn.microsoft.com/en-us/library/kw1tezhk%28v=vs.94%29.aspx>
>>>
>>> http://programmers.stackexchange.com/questions/
>>> 16528/single-statement-if-block-braces-or-no
>>> http://publib.boulder.ibm.com/infocenter/comphelp/v7v91/
>>> index.jsp?topic=%2Fcom.ibm.vacpp7a.doc%2Flanguage%2Fref%2Fclrc08csor.htm
>>> http://msdn.microsoft.com/en-us/library/ms173143.aspx
>>>
>>> and so on across multiple languages.  Whether or not you think these
>>> forms should be different, programmers don't expect them to differ.
>>>
>>
>> This is all beside the point, since the unbraced let as consequent of if
>> cannot make a useful binding (if you use comma-separated multiple
>> declarators, you still can't use any of the values that initialize the
>> bindings except in later useless-outside-the-single-declaration
>> consequent).
>>
>> /be
>>
>
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