matchFirstRegex(str, re) {
    var m;
    while ((m = re.exec(str)) !== null) {
      if (m.index === re.lastIndex) {
        re.lastIndex++;
      }
      return m;
    }
  }
get first regex and return
@param  {string} str content
@param  {regex}  re  regexobj
@return {match}      match object