code: function indexOfMatch(string, regex, index) {
    const str = index !== null ? string.substring(index) : string;
    const matches = str.match(regex);
    return matches ? str.indexOf(matches[0]) + index : -1;
  }
docs: Finds the first index based on a regex match
  @param   {RegExp} regex a regex object
  @param   {Number} index optional starting index
  @returns {Number} the index of the match