Intl.DateTimeFormat('de-CH', {year, month}) outputs different separators between Node 24.13.0 and 24.13.1 #61861
Description
Version
24.13.1
Platform
Darwin N22134 25.3.0 Darwin Kernel Version 25.3.0: Wed Jan 28 20:48:41 PST 2026; root:xnu-12377.81.4~5/RELEASE_ARM64_T6041 arm64
Subsystem
No response
What steps will reproduce the bug?
Intl.DateTimeFormat produces inconsistent formatting for partial date options (year + month) between Node 24.13.0 and 24.13.1.
• Node 24.13.0 outputs '12.2021' (dot separator) as expected for de-CH.
• Node 24.13.1 outputs '12/2021' (slash separator) for the same code.
• Adding day: '2-digit' produces consistent '07.12.2021' in both versions.
This behavior change breaks SSR/client hydration in frameworks like Next.js when formatting dates for de-CH locale.
Reproduction:
// Test partial month/year formatting
console.log(
new Intl.DateTimeFormat('de-CH', { year: 'numeric', month: '2-digit' }).format(new Date("2021-12-07"))
);
// Test full date formatting
console.log(
new Intl.DateTimeFormat('de-CH', { year: 'numeric', month: '2-digit', day: '2-digit' }).format(new Date("2021-12-07"))
);How often does it reproduce? Is there a required condition?
Always
What is the expected behavior? Why is that the expected behavior?
Both Node versions should produce '12.2021' for { year, month } in de-CH locale.
Separator should follow locale conventions consistently, even for partial formats.
What do you see instead?
Node 24.13.1 outputs '12/2021'
Additional information
No response