toLocaleDateString does not handle zh-CN properly

[FredrikL]

Version

16.14

Platform

MacOS 12.2.1 & Github Actions linux based runners

Subsystem

icu

What steps will reproduce the bug?

The following script can be used to reproduce

const dateWithTimeOptions = Object.freeze({
  year: 'numeric',
  month: '2-digit',
  day: '2-digit',
  hour: 'numeric',
  minute: 'numeric',
});

const localTime = Date.now();
const str = new Date(localTime).toLocaleDateString('zh-CN', dateWithTimeOptions);
console.log(str);

How often does it reproduce? Is there a required condition?

No response

What is the expected behavior?

Output with 16.13 (expected)
2022/02/17 下午3:42

What do you see instead?

Output with 16.14
2022/02/17 15:42

Additional information

No response

[richardlau]

This is almost certainly due to the update to ICU 70.1 (#41525) which was done to update the timezone information. In previous issues reporting formatting changes it has been stated by people more familiar with ICU that the exact format of locale strings should not be depended upon to remain invariant:

The purpose of the locale strings has always been to attempt to output something that will be readable to people with their own language and cultural preferences. Think of a general user viewing some financial information. As I mentioned, if your documents have a specific requirement, they fall somewhat outside of this.

Ref: #38897 (comment)
cc @nodejs/i18n-api

FWIW adding the hour12 formatting option produces consistent results between 16.14.0 and 16.13.0:

const dateWithTimeOptions = Object.freeze({
  year: 'numeric',
  month: '2-digit',
  day: '2-digit',
  hour: 'numeric',
  minute: 'numeric',
  hour12: true,
});

const localTime = Date.now();
const str = new Date(localTime).toLocaleDateString('zh-CN', dateWithTimeOptions);
console.log(str);

[srl295]

@FredrikL specifically, CLDR-10560

consensus was:

For CN, strongly prefer 24-hour time, HH:mm. Many many examples provided to suggest that this now the most common form for times in text (though not necessarily in informal speech)

Definitely use hour12 as suggested to request a specific cycle format, but be aware that it is not considered the recommended cycle for this locale.

[srl295]

FYI (and @richardlau perhaps this could be made more prominent somewhere) : the CLDR project has delta charts, accessible by https://cldr.unicode.org/index/charts - you can see what changed from release to release.

[srl295]

not a bug, closing