Intl.Locale.prototype.getWeekInfo().firstDay replacement function

getStartOfWeekByLocale.ts

const LOCALES_TO_START_OF_WEEK = {
    'af-ZA': 7,
    'am-ET': 7,
    'ar-AE': 1,
    'ar-BH': 6,
    'ar-DZ': 1,
    'ar-EG': 6,
    'ar-IQ': 6,
    'ar-JO': 7,
    'ar-KW': 6,
    'ar-LB': 1,
    'ar-LY': 6,
    'ar-MA': 1,
    'arn-CL': 1,
    'ar-OM': 6,
    'ar-QA': 6,
    'ar-SA': 7,
    'ar-SD': 6,
    'ar-SY': 6,
    'ar-TN': 1,
    'ar-YE': 7,
    'as-IN': 7,
    'az-az': 1,
    'az-Cyrl-AZ': 1,
    'az-Latn-AZ': 1,
    'ba-RU': 1,
    'be-BY': 1,
    'bg-BG': 1,
    'bn-BD': 7,
    'bn-IN': 7,
    'bo-CN': 7,
    'br-FR': 1,
    'bs-Cyrl-BA': 1,
    'bs-Latn-BA': 1,
    'ca-ES': 1,
    'co-FR': 1,
    'cs-CZ': 1,
    'cy-GB': 1,
    'da-DK': 1,
    'de-AT': 1,
    'de-CH': 1,
    'de-DE': 1,
    'de-LI': 1,
    'de-LU': 1,
    'dsb-DE': 1,
    'dv-MV': 5,
    'el-CY': 1,
    'el-GR': 1,
    'en-029': 1,
    'en-AU': 1,
    'en-BZ': 7,
    'en-CA': 7,
    'en-cb': 1,
    'en-GB': 1,
    'en-IE': 1,
    'en-IN': 7,
    'en-JM': 7,
    'en-MT': 7,
    'en-MY': 1,
    'en-NZ': 1,
    'en-PH': 7,
    'en-SG': 7,
    'en-TT': 7,
    'en-US': 7,
    'en-ZA': 7,
    'en-ZW': 7,
    'es-AR': 1,
    'es-BO': 1,
    'es-CL': 1,
    'es-CO': 7,
    'es-CR': 1,
    'es-DO': 7,
    'es-EC': 1,
    'es-ES': 1,
    'es-GT': 7,
    'es-HN': 7,
    'es-MX': 7,
    'es-NI': 7,
    'es-PA': 7,
    'es-PE': 7,
    'es-PR': 7,
    'es-PY': 7,
    'es-SV': 7,
    'es-US': 7,
    'es-UY': 1,
    'es-VE': 7,
    'et-EE': 1,
    'eu-ES': 1,
    'fa-IR': 6,
    'fi-FI': 1,
    'fil-PH': 7,
    'fo-FO': 1,
    'fr-BE': 1,
    'fr-CA': 7,
    'fr-CH': 1,
    'fr-FR': 1,
    'fr-LU': 1,
    'fr-MC': 1,
    'fy-NL': 1,
    'ga-IE': 1,
    'gd-GB': 1,
    'gd-ie': 1,
    'gl-ES': 1,
    'gsw-FR': 1,
    'gu-IN': 7,
    'ha-Latn-NG': 1,
    'he-IL': 7,
    'hi-IN': 7,
    'hr-BA': 1,
    'hr-HR': 1,
    'hsb-DE': 1,
    'hu-HU': 1,
    'hy-AM': 1,
    'id-ID': 7,
    'ig-NG': 1,
    'ii-CN': 7,
    'in-ID': 7,
    'is-IS': 1,
    'it-CH': 1,
    'it-IT': 1,
    'iu-Cans-CA': 7,
    'iu-Latn-CA': 7,
    'iw-IL': 7,
    'ja-JP': 7,
    'ka-GE': 1,
    'kk-KZ': 1,
    'kl-GL': 1,
    'km-KH': 7,
    'kn-IN': 7,
    'kok-IN': 7,
    'ko-KR': 7,
    'ky-KG': 1,
    'lb-LU': 1,
    'lo-LA': 7,
    'lt-LT': 1,
    'lv-LV': 1,
    'mi-NZ': 1,
    'mk-MK': 1,
    'ml-IN': 7,
    'mn-MN': 1,
    'mn-Mong-CN': 7,
    'moh-CA': 7,
    'mr-IN': 7,
    'ms-BN': 1,
    'ms-MY': 1,
    'mt-MT': 7,
    'nb-NO': 1,
    'ne-NP': 7,
    'nl-BE': 1,
    'nl-NL': 1,
    'nn-NO': 1,
    'no-no': 1,
    'nso-ZA': 7,
    'oc-FR': 1,
    'or-IN': 7,
    'pa-IN': 7,
    'pl-PL': 1,
    'prs-AF': 6,
    'ps-AF': 6,
    'pt-BR': 7,
    'pt-PT': 7,
    'qut-GT': 7,
    'quz-BO': 1,
    'quz-EC': 1,
    'quz-PE': 7,
    'rm-CH': 1,
    'ro-mo': 7,
    'ro-RO': 1,
    'ru-mo': 7,
    'ru-RU': 1,
    'rw-RW': 1,
    'sah-RU': 1,
    'sa-IN': 7,
    'se-FI': 1,
    'se-NO': 1,
    'se-SE': 1,
    'si-LK': 1,
    'sk-SK': 1,
    'sl-SI': 1,
    'sma-NO': 1,
    'sma-SE': 1,
    'smj-NO': 1,
    'smj-SE': 1,
    'smn-FI': 1,
    'sms-FI': 1,
    'sq-AL': 1,
    'sr-BA': 1,
    'sr-CS': 1,
    'sr-Cyrl-BA': 1,
    'sr-Cyrl-CS': 1,
    'sr-Cyrl-ME': 1,
    'sr-Cyrl-RS': 1,
    'sr-Latn-BA': 1,
    'sr-Latn-CS': 1,
    'sr-Latn-ME': 1,
    'sr-Latn-RS': 1,
    'sr-ME': 1,
    'sr-RS': 1,
    'sr-sp': 1,
    'sv-FI': 1,
    'sv-SE': 1,
    'sw-KE': 7,
    'syr-SY': 6,
    'ta-IN': 7,
    'te-IN': 7,
    'tg-Cyrl-TJ': 1,
    'th-TH': 7,
    'tk-TM': 1,
    'tlh-QS': 1,
    'tn-ZA': 7,
    'tr-TR': 1,
    'tt-RU': 1,
    'tzm-Latn-DZ': 1,
    'ug-CN': 7,
    'uk-UA': 1,
    'ur-PK': 7,
    'uz-Cyrl-UZ': 1,
    'uz-Latn-UZ': 1,
    'uz-uz': 1,
    'vi-VN': 1,
    'wo-SN': 1,
    'xh-ZA': 7,
    'yo-NG': 1,
    'zh-CN': 7,
    'zh-HK': 7,
    'zh-MO': 7,
    'zh-SG': 7,
    'zh-TW': 7,
    'zu-ZA': 7,
}

/**
 * Returns the start of the week for the given locale
 * We need this implementation because currently Intl.Locale.prototype.getWeekInfo() is supported only in Safari (2023-10-23)
 * @param {string} locale locale ID
 * @returns {number} 1 for Monday, 7 for Sunday.
 */
export const getStartOfWeekByLocale = (locale: string): number => LOCALES_TO_START_OF_WEEK[locale] || 1