> On Oct 14, 2016, at 11:02 AM, Claude Pache <claude.pa...@gmail.com> wrote:
> 
> 
>> Le 11 oct. 2016 à 11:07, medikoo <medikoo+mozilla....@medikoo.com> a écrit :
>> 
>> I was searching the archived but wasn't able to find the answer.
>> 
>> What's the reasoning behind having Number(symbol) crash instead of returning
>> NaN (as it's in case all other non-coercible values?). It feels not
>> consistent.
>> 
>> If someone can point me to some discussion that provided the reasoning I'd
>> be grateful
>> 
> 
> I believe that the reason of the inconsistency is more an accident of history 
> in the development of ES6 than a well-reasoned design decision. Here is my 
> understanding:

No this was an intentional design decision. There is no  obvious or natural 
Number value corresponding to symbol values. Rather than inventing some 
arbitrary conversion rule (for example producing NaN) TC39 choose to throw an 
exception for such conversions as they are a clear manifestation of some sort 
of program bug.

Note that the coercion rules for the original JS primitive types were created 
at a time when JavaScript did not have an exception handling mechanism and 
hence all operations were required to produce some value. Throwing exceptions 
for unreasonable Symbol coercions is intentionally inconsistent with the 
handling of the original primitive coercions and is intended to set a new 
precedent  that will be applied to any other new primitive types that might be 
added to ES in the future.

Allen
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