NumberFormat maxSignificantDigits Limit

Logan Smyth loganfsmyth at gmail.com
Sun Jan 20 21:47:46 UTC 2019


It does seem unclear why the limit is 21. Is that maybe the most you need
to uniquely stringify any double value?

> an only encode up to 17 significant decimal digits

That's true for decimal values, but the limit of 21 would also include the
fractional portion of the double value as well, so would need more than 17,
I think?

On Sun, Jan 20, 2019 at 1:18 PM Isiah Meadows <isiahmeadows at gmail.com>
wrote:

> I feel this is probably best asked at https://github.com/tc39/ecma402,
> since it seems to imply a potential spec bug.
>
> -----
>
> Isiah Meadows
> contact at isiahmeadows.com
> www.isiahmeadows.com
>
>
> On Sun, Jan 20, 2019 at 2:31 PM Anders Rundgren <
> anders.rundgren.net at gmail.com> wrote:
>
>> On 2019-01-20 20:18, Ethan Resnick wrote:
>> > Hi,
>> >
>> > Apologies if es-discuss is the wrong venue for this; I've tried first
>> poring through the specs and asking online to no avail.
>> >
>> > My question is: why is the limit for the `maximumSignificantDigits`
>> option in the `NumberFormat` API set at 21? This seems rather arbitrary —
>> and especially odd to me given that, iiuc, all Numbers in JS, as 64 bit
>> floats, can only encode up to 17 significant decimal digits. Is this some
>> sort of weird historical artifact of something? Should the rationale be
>> documented anywhere?
>>
>> I don't know for sure but if you input this in a browser debugger it will
>> indeed respond with the same 21 [sort of] significant digits
>> 999999999999999900000
>>
>> rgds,
>> Anders
>> >
>> > Thanks!
>> >
>> > Ethan
>> >
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