Zlúčiť bunky v dynamickej tabulky jquery

  <script src="https://code.jquery.com/jquery-1.10.2.js"></script>
        
        <style>
        table td {
    border:1px solid #ddd;
    height:30px;
    -moz-user-select:none;
    -webkit-user-select:none;
    user-select:none;
}
.selected {
    background:#69c;
}
table {
    width:100%;
    border-collapse:collapse;
}
</style>
        <script>
        window.onload = function () {
        $('td').mousedown(function () {
    $(this).closest('table').find('td').removeClass('selected');
     start = {
        x: this.cellIndex,
        y: this.parentNode.rowIndex
    }
    $(this).closest('table').find('td').mouseover(function () {
        x1 = Math.min(start.x, this.cellIndex);
       y1 = Math.min(start.y, this.parentNode.rowIndex);
         x2 = Math.max(start.x, this.cellIndex);
        y2 = Math.max(start.y, this.parentNode.rowIndex);

        $(this).closest('table').find('td').each(function () {
           x = this.cellIndex;
             y = this.parentNode.rowIndex;

            if (x >= x1 && x <= x2 && y >= y1 && y <= y2) {
                $(this).addClass('selected');
                        
            } else {
                $(this).removeClass('selected');
            }
        });
    });
     self = this;
    $(document).mouseup(function () {
        $(self).closest('table').find('td').unbind('mouseover');

        $(document).unbind('mouseup');

    });

})
        $("#merge").click(function () {
//code here
/*td.setAttribute('rowspan', rows);
td.setAttribute('colspan',columns);*/

alert("code here for rowspan and colspan cells")

   
});
}
 </script>

<input type="button" id="merge"  value="Merge Cells">

<table align="left" height="200" border="1" bordercolor="0" cellpadding="2" 
cellspacing="2" width="200">
<tbody>
<tr>
<td height="20" width="40">
</td>
<td height="20" width="40">
</td>
<td height="20" width="40"></td>
<td height="20" width="40">
</td>
</tr>
<tr>
<td height="20" width="40"></td>
<td height="20" width="40"></td>
<td height="20" width="40"></td>
<td height="20" width="40"></td>
</tr>
<tr>
<td height="20" width="40"></td>
<td height="20" width="40"></td>
<td height="20" width="40">
</td><td height="20" width="40"></td>
</tr>
<tr>
<td height="20" width="40"></td>
<td height="20" width="40">
</td><td height="20" width="40"></td>
<td height="20" width="40"></td>
</tr>
</tbody>
</table>&nbsp;