Calculate Total By Javascript In Gridview With Paging?

Without paging function, i can loop through the gridview by using

var sum = 0;
var gridViewCtlId = '<%=timesheetView.ClientID%>';
var grid = document.getElementById(gridViewCtlId);
var gridLength = grid.rows.length;

so with gridLength i can loop through the gridview to sum all rows. However, when I use paging event of gridview, i use the page size to loop through all rows, but it occurs errors because the last page may not have enough rows.