Detecting browser locale for SimpleLocalize.io

detectBrowserLocale.ts

export const LOCALE_PATTERN = /[a-z]{2}_[A-Z]{2}/gi;

export const isLocaleValid = (locale: string): boolean => {
  return Boolean(new RegExp(LOCALE_PATTERN).test(locale));
}

export const getBrowserLocaleOrNull = (): string | null => {
 
  const locale = window.navigator.language; //won't work on SSR
  if (!locale) {
    return null;
  }

  if (locale.length === 2) {
    if(locale === "en") {
      return "en_US";
    }
    return `${locale}_${locale.toUpperCase()}`;
  }
  
  if (locale.length === 4 && locale.includes("-")) {
    return locale.replace(/-/g, "_");
  }

  return null;
}