js操作table

<script type="text/javascript">
    var form = document.forms["form1"];
    var table = document.getElementById("myTable");
    var selectBox = table.getElementsByTagName("input");
    var tr = table.getElementsByTagName("tr");
    var clicked = true;
        function insert_row(){
          //alert(table.rows[0].cells.length)
var thisrow = table.insertRow(0);
          var thiscell = thisrow.insertCell(0);
          thiscell.innerHTML = "<input type=\"checkbox\" name=\"checkbox10\" value=\"checkbox\" />";
          var thiscell1 = thisrow.insertCell(1);
          thiscell1.innerHTML = "cell";
          var thiscell2 = thisrow.insertCell(2);
          thiscell2.innerHTML = "cell";
          var thiscell3 = thisrow.insertCell(3);
          thiscell3.innerHTML = "cell";
          var thiscell4 = thisrow.insertCell(4);
          thiscell4.innerHTML = "cell";
          thiscell4.align = "center";
           
        }
        function insert_Cell(){
            var y = table.rows[0].insertCell(0);
            y.colSpan="2";
            y.innerHTML = "sssss";
        }
        function selectall(){
            for(i=0;i<selectBox.length;i++){
                selectBox[i].checked = true;
            }
        }
        function noselect(){
            for(i=0;i<selectBox.length;i++){
                selectBox[i].checked = false;
            }
        }
        function inverse(){
            for(i=0;i<selectBox.length;i++){
                if(selectBox[i].checked){
                    selectBox[i].checked = false;
                }else{
                    selectBox[i].checked = true;
                }
            }
        }
        function delRow(){
            for(i=selectBox.length-1;i>=0;i--){
                //alert(typeof(selectBox[i]));
if(selectBox[i].checked){
                    table.deleteRow(i);
                }
            }
        }
        function onRefresh(){
            location.reload();
        }
        function copyRow(){
            for(i=0;i<selectBox.length;i++){
                if(selectBox[i].checked){
                    //var copytable = document.getElementById("copyTable");
var tablerow = table.insertRow(table.rows.length);
                    tablerow.innerHTML = table.rows[i].innerHTML;
                }
            }
        }
        function tableAlign(){
            for(i=0;i<selectBox.length;i++){
                if(selectBox[i].checked && clicked){
                    table.rows[i].align = "center";
                }
            }
        }
        function changeColor(){
            var skip = true;
            for(i=0;i<tr.length;i++){                
                if(skip){
                    tr[i].bgColor = "#cccccc";
                    skip = false;
                }else{
                    tr[i].bgColor = "#ffffff";
                    skip = true;
                }
            }
        }
 
</script>