Tag Operations

/**
 * Check whether a hyphen-separated tag is valid and well-formed. Always returns a Tag object.
 * @param {string} tag - The language tag to validate (e.g., "en-US", "zh-Hans-CN")
 * @returns {Tag} Tag instance for detailed analysis
 */
function tags(tag: string): Tag;

import { tags } from "language-tags";

// Validate various tag formats
const simple = tags("en");
console.log(simple.valid()); // true
console.log(simple.format()); // "en"

const complex = tags("zh-hans-cn");
console.log(complex.valid()); // true
console.log(complex.format()); // "zh-Hans-CN"

const invalid = tags("invalid-tag-format");
console.log(invalid.valid()); // false
console.log(invalid.errors()); // Array of Error objects

/**
 * Shortcut for tags(tag).valid(). Returns true if the tag is valid, false otherwise.
 * @param {string} tag - The language tag to check
 * @returns {boolean} True if valid, false otherwise
 */
function check(tag: string): boolean;

import { check } from "language-tags";

// Quick validation checks
console.log(check("en-US")); // true
console.log(check("fr-CA")); // true
console.log(check("invalid")); // false
console.log(check("en-XYZ")); // false (XYZ is not a valid region)

/**
 * Check if the tag is valid according to BCP 47 standards
 * @returns {boolean} True if valid, false otherwise
 */
valid(): boolean;

/**
 * Get detailed validation errors if the tag is invalid
 * @returns {Error[]} Array of Error objects with validation details
 */
errors(): Error[];

/**
 * Get all subtags that make up this tag
 * @returns {Subtag[]} Array of Subtag objects
 */
subtags(): Subtag[];

/**
 * Get the language subtag (first component)
 * @returns {Subtag|null} Language subtag or null if not found
 */
language(): Subtag | null;

/**
 * Get the region subtag 
 * @returns {Subtag|null} Region subtag or null if not found
 */
region(): Subtag | null;

/**
 * Get the script subtag
 * @returns {Subtag|null} Script subtag or null if not found
 */
script(): Subtag | null;

/**
 * Find a subtag of the specified type
 * @param {string} type - Type to search for ("language", "region", "script", "variant", etc.)
 * @returns {Subtag|null} Matching subtag or null if not found
 */
find(type: string): Subtag | null;

/**
 * Get the tag type
 * @returns {string} "grandfathered", "redundant", or "tag"
 */
type(): string;

/**
 * Get descriptions for the tag
 * @returns {string[]} Array of description strings
 */
descriptions(): string[];

/**
 * Get the preferred tag if this tag is deprecated
 * @returns {Tag|null} Preferred Tag object or null if not deprecated
 */
preferred(): Tag | null;

/**
 * Get the deprecation date if the tag is deprecated
 * @returns {string|null} Date string or null if not deprecated
 */
deprecated(): string | null;

/**
 * Get the date when this tag was added to the registry
 * @returns {string|undefined} Date string in YYYY-MM-DD format or undefined if not available
 */
added(): string | undefined;

/**
 * Format the tag according to RFC 5646 case conventions
 * @returns {string} Properly formatted tag string
 */
format(): string;

import { tags } from "language-tags";

const tag = tags("zh-hans-cn");

// Component access
console.log(tag.language().format()); // "zh"
console.log(tag.script().format()); // "Hans"
console.log(tag.region().format()); // "CN"

// Information
console.log(tag.type()); // "tag"
console.log(tag.valid()); // true
console.log(tag.format()); // "zh-Hans-CN"

// All subtags
const subtags = tag.subtags();
subtags.forEach(subtag => {
  console.log(`${subtag.type()}: ${subtag.format()}`);
});
// Output:
// language: zh
// script: Hans  
// region: CN

static ERR_DEPRECATED = 1;        // Tag is deprecated
static ERR_NO_LANGUAGE = 2;       // No language subtag found
static ERR_UNKNOWN = 3;           // Unknown subtag
static ERR_TOO_LONG = 4;          // Subtag too long
static ERR_EXTRA_REGION = 5;      // Multiple region subtags
static ERR_EXTRA_EXTLANG = 6;     // Multiple extlang subtags
static ERR_EXTRA_SCRIPT = 7;      // Multiple script subtags
static ERR_DUPLICATE_VARIANT = 8; // Duplicate variant subtags
static ERR_WRONG_ORDER = 9;       // Subtags in wrong order
static ERR_SUPPRESS_SCRIPT = 10;  // Script should be suppressed
static ERR_SUBTAG_DEPRECATED = 11; // Contains deprecated subtag
static ERR_EXTRA_LANGUAGE = 12;   // Multiple language subtags

import { tags, Tag } from "language-tags";

const invalidTag = tags("en-US-US"); // Multiple regions
const errors = invalidTag.errors();

errors.forEach(error => {
  if (error.code === Tag.ERR_EXTRA_REGION) {
    console.log("Multiple region subtags detected");
    console.log(`Tag: ${error.tag}`);
  }
});