<script language=javascript type="text/javascript">
function getClick()
{
    var c=document.getElementById("<%=TextBox1.ClientID %>");
    if(c.IsNotNull == 1)
    {
        alert("IsNotNull is 1");
    }
    else if(c.IsNotNull == 0)
    {
        alert("IsNotNull is 0");
    }
    else
    {
        alert(c.IsNotNull); //不是0或者1時會顯示IsNotNull的屬性值
    }
}
</script>