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>