Asp.Net การส่งค่าจาก JavaScript ไปใช้ใน Asp.Net

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

var temp = ['21-3-2013' , '22-3-2013' , '23-3-2013']
document.getElementById("<%=Postvalue.ClientID%>").value = temp;

 Protected Sub btnSave_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSave.Click
        Dim temp As String = Postvalue.Value
        alert(temp)
    End Sub