Add suffix to TextBox on TextChange using C# and VB.Net in ASP.Net

Hi BugHunter,

Refer below sample.

HTML

Name :
<asp:TextBox runat="server" ID="txtName" AutoPostBack="true" OnTextChanged="AddString" />

Code

C#

protected void AddString(object sender, EventArgs e)
{
    string addSuffix = "@domain.com";
    txtName.Text += addSuffix;
}

VB.Net

Protected Sub AddString(ByVal sender As Object, ByVal e As EventArgs)
    Dim addSuffix As String = "@domain.com"
    txtName.Text += addSuffix
End Sub

Screenshot