code: function hexNumber(char) {
      var code = char.toLowerCase().charCodeAt(0);
      // 0-9
      if (code >= 48 && code <= 57) {
        return code - 48;
      }
      // a-f
      if (code >= 97 && code <= 102) {
        return code - 87;
      }
      return code;
    }
docs: /*
  @desc convert hex char to number
  @param {String} 0-9a-fA-F
  @return {Number}