requireValidLocale
function requireValidLocale(
value: string | null | undefined,
message: string = "Expected a valid locale."
): string;
Exactly two ASCII letters, in either case — "en", "UK". A region or a script subtag, as in "en-US", is rejected: this is the short language code, not a full BCP 47 tag.
isX and nonX answer a question and never interrupt control flow; requireX and requireNonX hand the value back or throw. The scheme is explained in Validation conventions.
Parameters
Parameter | Type | Description |
|---|---|---|
|
| The value to validate. |
|
| The message of the exception. A default is used when omitted. |
Returns
string — the same value, typed as a locale code.
Throws
Exception | Condition |
|---|---|
| the value is not a locale code. |
Examples
What passes and what does not
requireValidLocale("en"); // => "en"
requireValidLocale("UK"); // => "UK"
requireValidLocale("en-US"); // throws IllegalArgumentException
requireValidLocale("eng"); // throws IllegalArgumentException
See also
Source
23 September 2026
This documentation was generated with AI (Claude) from the library's source code.