<input type="checkbox" name="a" value="1" /><br/>

<input type="checkbox" name="a" value="2" /><br/>

<input type="checkbox" name="a" value="3" /><br/>

<input type="checkbox" name="a" value="4" /><br/>

<input type="button" onclick="changeIds()" />

<script type="text/javascript">

    checkedIds="";//翻页保存选中的id

          function changeIds(){

               var oneches=document.getElementsByName("a");

             for(var i=0;i<oneches.length;i++){

                 if(oneches[i].checked==true){

                     //避免重复累计id （不含该id时进行累加）

                     if(checkedIds.indexOf(oneches[i].value)==-1){

                         checkedIds=checkedIds+oneches[i].value+",";

                     }

                 }

                 if(oneches[i].checked==false){

                     //取消复选框时 含有该id时将id从全局变量中去除

                     if(checkedIds.indexOf(oneches[i].value)!=-1){

                         checkedIds=checkedIds.replace((oneches[i].value+","),"");

                     }

                 }

             }

             alert(checkedIds);

          }

    function getChecked(){

        checkedIds = '4,1,';

                var oneches=document.getElementsByName("a");

             for(var i=0;i<oneches.length;i++){

                     //全局变量中含有id，则该复选框选中

                     if(checkedIds.indexOf(oneches[i].value)!=-1){

                         oneches[i].checked=true;

                     }

                 }

                 alert(checkedIds);

          }

getChecked();

</script>