How to give space after 4 characters to an TextBox input as well as retrict alphabets.

We have a TextBox as :-

      <asp:TextBox ID="txtCardNumber" class="cardnumber" runat="server" 
             onkeyup="GiveSpace(this,4)" MaxLength="20" ></asp:TextBox>

Write the javascript function as :-

            <script type="text/javascript">
                    function GiveSpace(textboxid, spaceafter) {
                    spaceafter = spaceafter|| 4;
                 var v = textboxid.value.replace(/[^\dA-Z]/g, ''),
                  reg = new RegExp(".{" + spaceafter+ "}", "g")
                 textboxid.value = v.replace(reg, function (a, b, c) {
                 return a + ' ';
                  });
                 }
              </script>

This will restrict alphabets as well as give a space after every 4 numbers we enter in a textbox.

Note:- Very useful on the payment page when we ask for the credit card number.