isValid

The isValid function is a simple utility that checks if a string is a valid BCP-47 language tag according to both syntax rules and registry validation.

Signature

function isValid(tag: string, options?: ValidationOptions): boolean;

Description

isValid provides a convenient way to perform a complete validation of a BCP-47 language tag. It returns a boolean result indicating whether the tag is valid, rather than the detailed result object that validateLanguageTag returns.

Internally, this function calls validateLanguageTag and returns its isValid property.

Parameters

Parameter	Type	Required	Description
tag	string	Yes	The language tag to validate
options	ValidationOptions	No	Options for validation behavior

ValidationOptions

Option	Type	Default	Description
checkRegistry	boolean	true	Whether to validate subtags against registries
warnOnDeprecated	boolean	true	Whether to generate warnings for deprecated subtags
warnOnRedundantScript	boolean	true	Whether to generate warnings for redundant script subtags

Returns

• true if the tag is both syntactically well-formed and all subtags exist in their respective registries
• false if the tag is malformed or contains unknown subtags

Examples

import { isValid } from "ally-bcp-47";

// Valid language tags
isValid("en"); // true
isValid("en-US"); // true
isValid("zh-Hans-CN"); // true
isValid("de-AT-1996"); // true

// Invalid due to syntax errors
isValid("en-"); // false - empty subtag
isValid("en--US"); // false - double hyphen
isValid("123"); // false - language must start with a letter

// Invalid due to registry errors
isValid("en-ZZ"); // false - ZZ is not a valid region code
isValid("qq"); // false - qq is not a valid language code
isValid("en-Wxyz"); // false - Wxyz is not a valid script code

// Syntax-only validation
isValid("en-ZZ", { checkRegistry: false }); // true - valid syntax, registry validation disabled

Usage Notes

When to Use

• Use isValid when you need a simple boolean validation result
• Perfect for validation in form inputs, data import checks, or UI feedback
• Use when you don't need detailed error information

When to Use validateLanguageTag Instead

• When you need to know why a tag is invalid
• When you need to access the parsed tag components
• When you want to collect warnings as well as errors

Related Functions

• validateLanguageTag - For detailed validation results
• isWellFormed - For syntax-only validation
• parseTag - For parsing a tag into its components

Implementation Details

function isValid(tag: string, options?: ValidationOptions): boolean {
  const result = validateLanguageTag(tag, options);
  return result.isValid;
}