To demonstrate what I am doing I placed everything in one Javascript function.

function WebDataGrid1_RowSelectionChanged(webDataGrid, evntArgs) {
    document.getElementById('<%= HiddenField_SelectedRowIndex.ClientID %>').value = evntArgs.getSelectedRows().getItem(0).get_dataKey();
           
    var grid = var grid = $find('<%= WebDataGrid1.ClientID %>').get_rows();
    var row = grid.get_rowFromKey(document.getElementById('<%= HiddenField_SelectedRowIndex.ClientID %>').value);
    alert('Cell 0 in row should be = ' + row.get_cell(0).get_element().innerText);
}

When I select a row in the WebDataGrid, The datakey value of the selected row is stored into a hidden value, when I check on that, the hidden value is indeed holding the datakey value.

Now, I have a button somewhere on the page that I will press, The javascript function there will find the Grid and get the row collection, the next lines you can follow, but what I do, even if I place the value hardcoded the grid.get_rowFromKey keeps resolving to null.

Any idea what I am missing?