js弹出模式对话框,并接收回传值的方法

<script type="text/javascript">
    function openDialog(){
        paramers="dialogWidth:500px; dialogHeight:300px; status:no";
        workerId = window.showModalDialog("userList.aspx","",paramers);
        if(workerId!=undefined && workerId!=""){
            document.getElementById("leader").value = workerId;
          }
        }
</script>

<input type="button" value="选择" onclick="javascript:selectPositionAndClose();"/>

    </form>
<script type="text/javascript">
    function selectPositionAndClose(){
        var obj = document.getElementById("userList");

        var user = "";
        for(var i=0;i<obj.options.length;i++){

            if(obj.options[i].selected==true){
                user = obj.options[i].value;
            }
        }

        window.returnValue = user;
        window.close();
    }
</script>