callback = JS("
        /* code for columns on hover */
        table.on('mouseenter', 'td', function() {
        var row=table.cell(this).index().row;
        var col=table.cell(this).index().columnVisible;
        var full_text = row + ','+ col
        $('td[row][col]).attr('title', full_text);
        Shiny.onInputChange('hoverIndexJS', row);
            });"
       )