An "Object doesn't support property or method 'indexOf'" exception is thrown on "Select All" checkbox click in IE11

[DX Support team: this ticket was cloned from How to implement "Select All" checkbox which selects only rows with a visible SelectCheckBox?]
OK, I just tested it the following script in all browsers, but I get "Error: Object doesn't support property or method 'indexOf' in Internet Explorer 11.  It works on my local machine when I run it in IE where I am using DevExpress 12.1.4.0

ASPx
<script type="text/javascript">  
      function OnAllCheckedChanged(s, e) {  
          grid.PerformCallback(s.GetChecked());  
      }  

      function OnPageCheckedChanged(s, e) {  
          var indexes = grid.cpIndexesUnselected;  
          var topVisibleIndex = grid.GetTopVisibleIndex();  
          if (s.GetChecked()) {  
              //Select All Rows On Page();  
              for (var i = topVisibleIndex; i < topVisibleIndex + grid.cpPageSize; i++) {  
                  if (indexes.indexOf(i) == -1) //ERROR Happens HERE  
                      grid.SelectRowOnPage(i, true);  
              }  
          }  
          else  
              //Deselect All Rows On Page();  
              for (var i = topVisibleIndex; i < topVisibleIndex + grid.cpPageSize; i++) {  
                  if (indexes.indexOf(i) == -1) //ERROR Happens HERE  
                      grid.SelectRowOnPage(i, false);  
              }  
      }  

      function setGridHeaderCheckboxes(s, e) {  
          //cbAll  
          var indexes = grid.cpIndexesSelected;  
          cbAll.SetChecked(s.GetSelectedRowCount() == Object.size(indexes));  

          //cbPage  
          var allEnabledRowsOnPageSelected = true;  
          var indexes = grid.cpIndexesUnselected;  
          var topVisibleIndex = grid.GetTopVisibleIndex();  
          for (var i = topVisibleIndex; i < topVisibleIndex + grid.cpPageSize; i++) {  
              if (indexes.indexOf(i) == -1)  
                  if (!grid.IsRowSelectedOnPage(i)) allEnabledRowsOnPageSelected = false;  
          }  
          cbPage.SetChecked(allEnabledRowsOnPageSelected);  
      }  

      function OnGridEndCallback(s, e) {  
          setGridHeaderCheckboxes(s, e);  
      }  

      function OnGridSelectionChanged(s, e) {  
          setGridHeaderCheckboxes(s, e);  
      }  

      Object.size = function (obj) {  
          var size = 0, key;  
          for (key in obj) {  
              if (obj.hasOwnProperty(key)) size++;  
          }  
          return size;  
      };  
  </script>