js弹窗

页面： 

<asp:Button ID="Button3" 
                OnClientClick="javascript:editItem('AddUser.aspx',330,520)" runat="server"
                Text="修改" BackColor="#3399FF" ForeColor="White" BorderStyle="None"
                Height="22px" onclick="Button3_Click" />

<asp:HiddenField ID="chklist" runat="server" />

JS:

function editItem(url, width, height) {
    var itemlist = document.getElementById("chklist").value;
    if (itemlist.length == 0) {
        alert("请至少选择1条数据");
        return;
    }
    var list = itemlist.split(",");
    if (list.length > 1) {
        alert("您只能选择1条数据进行操作!");
        document.getElementById("chklist").value = ""; ///////////////////////////////////////
        return;
    }
    else {
        window.showModalDialog(url + "?id=" + document.getElementById("chklist").value + "&type=1", null, "dialogWidth:" + width + "px;dialogHeight:" + height + "px;help:no;unadorned:no;resizable:no;status:no");
        document.getElementById("chklist").value = "";
        // window.location.reload(true);
    }
}

function chbItem() {
    var chblist = document.getElementsByName("chkItem");
    if (chblist.length > 0) {
        var rtn = "";
        for (var i = 0; i < chblist.length; i++) {
            if (chblist[i].checked) {
                rtn += chblist[i].value + ",";
            }
            else {
                continue;
            }
        }
        document.getElementById("chklist").value = rtn.substring(0, rtn.length - 1);
        //        alert(document.getElementById("chklist").value);
    }
    else {
        alert("您还没有选择！");
        return;
    }
}