282504 2024-11-02 22:47:55 -0700 `new Intl.Locale('und').language` returns `undefined`, not string `'und'` 2025-08-18 15:56:33 -0700 1 1 1 Unclassified WebKit JavaScriptCore WebKit Nightly Build Unspecified Unspecified RESOLVED DUPLICATE 295853 BrowserCompat, InRadar P2 Normal --- 1 lionel.rowe webkit-unassigned iKonnyaku40 karlcow vitor.roriz webkit-bug-importer ysuzuki oldest_to_newest 2072366 0 lionel.rowe 2024-11-02 22:47:55 -0700 `new Intl.Locale('und').language` (and other locales with a `language` of `und`) return `undefined`, rather than the expected string `'und'`. This behavior diverges from the ECMA-402 spec. Repro: ```js new Intl.Locale('xxx').language // 'xxx' (correct result) new Intl.Locale('und').language // undefined (expected 'und') ``` Per ECMA-402 spec: https://tc39.es/ecma402/#sec-Intl.Locale.prototype.language > 3. Return GetLocaleLanguage(loc.[[Locale]]). https://tc39.es/ecma402/#sec-getlocalelanguage > 1. Let baseName be GetLocaleBaseName(locale). > 2. Assert: The first subtag of baseName can be matched by the unicode_language_subtag Unicode locale nonterminal. > 3. Return the first subtag of baseName. Other browsers/engines: * Chromium/V8 suffers from the same issue, presumably with a similar cause: https://issues.chromium.org/issues/334251989 * Firefox has the correct behavior I guess the offending code path is this one? https://github.com/WebKit/WebKit/blob/635a079e5128f24a69f90de3141943153e46e5bb/Source/JavaScriptCore/runtime/IntlLocale.cpp#L489-L494 2072676 1 ysuzuki 2024-11-04 16:41:32 -0800 This is ICU issue around "und" support. 2072709 2 lionel.rowe 2024-11-04 18:36:46 -0800 (In reply to Yusuke Suzuki from comment #1) > This is ICU issue around "und" support. Apologies for ignorance, this is my first bug report here. Do you mean it's an issue in ICU itself? Or it's relating to a preexisting issue against WebKit's ICU implementation? Or something else? I don't think it can be an issue in ICU itself, as ICU doesn't specify how implementations should _represent_ the various semantics (i.e. there's nothing in ICU that says an "und" locale shouldn't be represented as having a nullish "language" field). The problem is rather that ECMA-402 specifies that `GetLocaleLanguage` should return the language subtag unchanged. From a userland perspective, I first encountered this bug by creating `new Intl.Locale('und')` and noticing that its `language` was `undefined`, then noting that the TypeScript types appeared to be wrong. But upon checking the spec, I realized it was the implementation that was wrong, not the TS types.  2074106 3 webkit-bug-importer 2024-11-09 21:48:13 -0800 <rdar://problem/139586863> 2137196 4 iKonnyaku40 2025-08-18 12:39:53 -0700 In the latest JSC, `new Intl.Locale('und').language` correctly returns "und". 2137252 5 karlcow 2025-08-18 15:54:31 -0700 Safari TP 125 new Intl.Locale('und').language undefined new Intl.Locale('xxx').language "xxx" Firefox Nightly 143.0 and Chrome Canary 141.0 new Intl.Locale('und').language "und" new Intl.Locale('xxx').language "xxx" 2137253 6 karlcow 2025-08-18 15:56:33 -0700 This has been fixed in Bug 295853 *** This bug has been marked as a duplicate of bug 295853 ***