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Temporal should not coerce fractionalSecondDigits #4038
Description
(originally posted by @gibson042 in #3966 (comment) on 2026-09-21)
Given that GetTemporalFractionalSecondDigitsOption is already out of sync with ECMA-4021, can we tighten it up to reject non-integer numbers rather than coercing them?
1. If _digitsValue_ is not a Number, then
1. If ? ToString(_digitsValue_) is not *"auto"*, throw a *RangeError* exception.
1. Return ~auto~.
- 1. If _digitsValue_ is not a finite Number, throw a *RangeError* exception.
- 1. Let _digitCount_ be floor(ℝ(_digitsValue_)).
- 1. If _digitCount_ is not in the inclusive interval from 0 to 9, throw a *RangeError* exception.
- 1. Return _digitCount_.
+ 1. Return ? SnapToInteger(_digitsValue_, ~reject~, 0, 9)Temporal is sufficiently new that it seems unlikely for such a normative change of unexpected input to disrupt existing code.
Footnotes
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in which e.g.
new Intl.DurationFormat("en", { seconds: "numeric", fractionalDigits: 9.1 }).resolvedOptions().fractionalDigitsthrows butnew Intl.DurationFormat("en", { seconds: "numeric", fractionalDigits: 8.9 }).resolvedOptions().fractionalDigitsis 8 because DefaultNumberOption checks ℝ(value) against bounds before flooring, cf. https://github.com/tc39/ecma402/issues/691 and https://github.com/tc39/ecma402/pull/908 ↩
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