parse-accept-language.ts

const ACCEPT_LANGUAGE_REGEX =
  /(?<code>[a-zA-Z]{1,8})(?:-(?<region>[a-zA-Z]{1,8}))?(?:;q=(?<quality>0\.\d+|\d))?/g;

type Language = {
  code: string;
  region?: string;
  quality: number;
};

export default function parseAcceptLanguage(header: string): Array<Language> {
  const result = new Array<Language>();
  let match: RegExpExecArray | null;
  while ((match = ACCEPT_LANGUAGE_REGEX.exec(header)) !== null) {
    if (match.groups) {
      const code = match.groups["code"];
      const region = match.groups["region"];
      const quality = match.groups["quality"]
        ? parseFloat(match.groups["quality"])
        : 1.0;
      result.push({ code, region, quality });
    }
  }
  return result;
}