Concatinate multiple regexs

concatRegex.ts

export const concatRegex = (...regexs: RegExp[]): RegExp => {
  const flags = Array.from(
    new Set<string>(
      regexs.join().split('')
    )
  ).join();
  return new RegExp(regexs.reduce((a, b) => a + b.source, ''), flags);
}