Further to above Answer, You can do validation on
onchange
Event of your
TextBox
using
Ajax.
<asp:textbox id="txtName" runat="server" onchange="javascript: Test();" />
You can refer my Tip/Trick for "
Asp.Net Ajax".
Simplifying-Asp-Net-Core-Ajax
Updated - Or use
onblur
JavaScript Event.
<asp:textbox id="txtName" runat="server" onblur="javascript: Test();" />