code: function columnsTotalWidth(columns, prop) {
      var totalWidth = 0;
      for (var _i = 0, columns_2 = columns; _i < columns_2.length; _i++) {
          var column = columns_2[_i];
          var has = prop && column[prop];
          totalWidth = totalWidth + (has ? column[prop] : column.width);
      }
      return totalWidth;
  }
docs: Calculates the total width of all columns and their groups