How corectlly merge cell in table with button

How corectlly merge cell in table with button

How to prevent that, when selected merged cells avoid errors of the merger. I do not speak English very well

thanks
  1.     <script src="http://code.jquery.com/jquery-1.9.1.js"></script>
    <style type="text/css">
            table{width: 80%;}
            table td{border: 1px solid #97B4D1;text-align: center;cursor:pointer;}
        </style>
        <script type="text/javascript">
            var StartTD = null;
            var StartIndex = null;
            var EndTD = null;
            var EndIndex = null;
            $(this).ready(function () {
                $("td").unbind("mousedown").bind("mousedown", function () {
                    $("table td").css("background-color", "");
                    StartTD = $(this);
                    var y = $(this).index();
                    var x = $(this).parent().index();
                    StartIndex = { x: x, y: y };
                });
                $("td").unbind("mouseup").bind("mouseup", function () {
                    EndTD = $(this);
                    var y = $(this).index();
                    var x = $(this).parent().index();
                    EndIndex = { x: x, y: y };
                    SelectTD(StartIndex, EndIndex, "green");
                });
                $("#btMerge").click(function () {
                    MergeCell(StartIndex, EndIndex);
                  MergeCell(EndIndex,StartIndex);
                });
            });
          
            function SelectTD(StartIndex, EndIndex,Color) {
                var MinX = null;
                var MaxX = null;
                var MinY = null;
                var MaxY = null;
                if (StartIndex.x < EndIndex.x) {
                    MinX = StartIndex.x; MaxX = EndIndex.x;

                }else {
                    MinX = EndIndex.x; MaxX = StartIndex.x;
                };
                if (StartIndex.y < EndIndex.y) {
                    MinY = StartIndex.y; MaxY = EndIndex.y;
                } else {
                    MinY = EndIndex.y; MaxY = StartIndex.y;
                };
                StartIndex = { x: MinX, y: MinY };
                EndIndex = { x: MaxX, y: MaxY };
                for (var i = MinX; i <= MaxX; i++) {
                    for (var j = MinY; j <= MaxY; j++) {
                        var SelectTR = $("table tr").eq(i);
                        $("td", SelectTR).eq(j).css("background-color", Color);
                    }
                }
            }
          
            function MergeCell(StartIndex, EndIndex) {
                var Colspan = null;
                var Rowspan = null;
                Rowspan = EndIndex.x - StartIndex.x + 1;
                Colspan = EndIndex.y - StartIndex.y + 1;
                var IndexTR = $("table tr").eq(StartIndex.x);
                $("td", IndexTR).eq(StartIndex.y).attr("colspan", Colspan).attr("rowspan", Rowspan);

                for (var i = StartIndex.x; i <= EndIndex.x; i++) {
                    for (var j = StartIndex.y; j <= EndIndex.y; j++) {
                        if (i == StartIndex.x && j == StartIndex.y) continue;
                        var SelectTR = $("table tr").eq(i);
                        $("td", SelectTR).eq(j).hide();
                    }
                }

            }
        </script>
    </head>
    <body>

        <input id="btMerge" type="button" value="Merge cells"/>
        <table cellspacing="0" cellpadding="0" border="0">
            <tr>
                <td>1</td>
                <td >2</td>
                <td>3</td>
                <td>4</td>
                <td>5</td>
            </tr>
            <tr>
                <td>1</td>
                <td>2</td>
                <td>3</td>
                <td>4</td>
                <td>5</td>
            </tr>
            <tr>
                <td>1</td>
                <td>2</td>
                <td>3</td>
                <td>4</td>
                <td>5</td>
            </tr>
             <tr>
                <td>1</td>
                <td >2</td>
                <td>3</td>
                <td>4</td>
                <td>5</td>
            </tr>
             <tr>
                <td>1</td>
                <td >2</td>
                <td>3</td>
                <td>4</td>
                <td>5</td>
            </tr>
        </table>
    </body>
    </html>