如何在Asp.net中使用Javascript从下拉列表中选择数据来设置标签文本属性

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<script type="text/javascript">
    function findDate() {
        var selectvalid = document.getElementById("<%=ddlvalid.ClientID  %>").value;
        if (selectvalid == "Select Validity") {
            alert("Please Select Validity");
        }
        else if (selectvalid == "Upto 7 Days") {
            var str = document.getElementById("<%=lblenqmdon.ClientID  %>").innerHTML;
            var parts = str.split('/');
            var month = parts[0] && parseInt(parts[0], 10);
            var day = parts[1] && parseInt(parts[1], 10);
            var year = parts[2] && parseInt(parts[2], 10);
            var duration = 7;
            if (day <= 31 && day >= 1 && month <= 12 && month >= 1) {
                var expiryDate = new Date(year, month - 1, day);
                expiryDate.setDate(expiryDate.getDate() + duration);
                var day = ('0' + expiryDate.getDate()).slice(-2);
                var month = ('0' + (expiryDate.getMonth() + 1)).slice(-2);
                var year = expiryDate.getFullYear();
                document.getElementById("<%=lblenddt.ClientID  %>").innerHTML = month + "/" + day + "/" + year;
            }
        }
        else if (selectvalid == "Upto 15 Days") {
            var str = document.getElementById("<%=lblenqmdon.ClientID  %>").innerHTML;
            var parts = str.split('/');
            var month = parts[0] && parseInt(parts[0], 10);
            var day = parts[1] && parseInt(parts[1], 10);
            var year = parts[2] && parseInt(parts[2], 10);
            var duration = 15;
            if (day <= 31 && day >= 1 && month <= 12 && month >= 1) {
                var expiryDate = new Date(year, month - 1, day);
                expiryDate.setDate(expiryDate.getDate() + duration);
                var day = ('0' + expiryDate.getDate()).slice(-2);
                var month = ('0' + (expiryDate.getMonth() + 1)).slice(-2);
                var year = expiryDate.getFullYear();
                document.getElementById("<%=lblenddt.ClientID  %>").innerHTML = month + "/" + day + "/" + year;
            }
        }
        else if (selectvalid == "Upto 30 Days") {
            var str = document.getElementById("<%=lblenqmdon.ClientID  %>").innerHTML;
            var parts = str.split('/');
            var month = parts[0] && parseInt(parts[0], 10);
            var day = parts[1] && parseInt(parts[1], 10);
            var year = parts[2] && parseInt(parts[2], 10);
            var duration = 30;
            if (day <= 31 && day >= 1 && month <= 12 && month >= 1) {
                var expiryDate = new Date(year, month - 1, day);
                expiryDate.setDate(expiryDate.getDate() + duration);
                var day = ('0' + expiryDate.getDate()).slice(-2);
                var month = ('0' + (expiryDate.getMonth() + 1)).slice(-2);
                var year = expiryDate.getFullYear();
                document.getElementById("<%=lblenddt.ClientID  %>").innerHTML = month + "/" + day + "/" + year;
            }
        }
    }
</script>
<script type="text/javascript">
    window.onload = function () {
        getDate();
    };
    function getDate() {
        var dt = new Date();
        var day = dt.getDate();
        var month = dt.getMonth() + 1;
        var year = dt.getFullYear();
        document.getElementById("<%=lblenqmdon.ClientID  %>").innerHTML = month + "/" + day + "/" + year;
    }
</script>

AND in Form

                <asp:DropDownList ID="ddlvalid" runat="server" onchange="javascript:findDate();">
                    <asp:ListItem>Select Validity</asp:ListItem>
                    <asp:ListItem>Upto 7 Days</asp:ListItem>
                    <asp:ListItem>Upto 15 Days</asp:ListItem>
                    <asp:ListItem>Upto 30 Days</asp:ListItem>
                </asp:DropDownList>

我设法做到了同样的这样-$(function () {

<script type="text/javascript">        
$("#ddlvalid").change(function () {
            var selectvalid = $("#ddlvalid option:selected").text();
            if (selectvalid == "Select Validity") {
                alert("Please Select Validity");
            }
            else if (selectvalid == "Upto 7 Days") {
                var today = new Date();
                var tomorrow = new Date(today);
                tomorrow.setDate(today.getDate() + 7);
                var dd = tomorrow.getDate();
                var mm = tomorrow.getMonth() + 1;
                var y = tomorrow.getFullYear();
                var output = tomorrow.getFullYear() + '/' + (mm < 10 ? '0' : '') + mm + '/' + (dd < 10 ? '0' : '') + dd;
                document.getElementById('lblenddt').innerHTML = output;
            }
            else if (selectvalid == "Upto 15 Days") {
                var today = new Date();
                var tomorrow = new Date(today);
                tomorrow.setDate(today.getDate() + 15);

                var dd = tomorrow.getDate();
                var mm = tomorrow.getMonth() + 1;
                var y = tomorrow.getFullYear();
                var output = tomorrow.getFullYear() + '/' + (mm < 10 ? '0' : '') + mm + '/' + (dd < 10 ? '0' : '') + dd;
                document.getElementById('lblenddt').innerHTML = output;
            }
            else if (selectvalid == "Upto 30 Days") {
                var today = new Date();
                var tomorrow = new Date(today);
                tomorrow.setDate(today.getDate() + 30);
                var dd = tomorrow.getDate();
                var mm = tomorrow.getMonth() + 1;
                var y = tomorrow.getFullYear();
                var output = tomorrow.getFullYear() + '/' + (mm < 10 ? '0' : '') + mm + '/' + (dd < 10 ? '0' : '') + dd;
                document.getElementById('lblenddt').innerHTML = output;
            }
        });
        window.onload = function show() {
            var d = new Date();
            var month = d.getMonth() + 1;
            var day = d.getDate();
            var output = d.getFullYear() + '/' + (month < 10 ? '0' : '') + month + '/' + (day < 10 ? '0' : '') + day;
            document.getElementById('lblenqmdon').innerHTML = output;
        };
    });
    </script>