Could you help me with this validation? The field "txtTelCel" should have the format #### - ####, where # is a numeric digit and if it is not in that format, a warning should appear informing the user.
Note: without using jQuery.
<label for="txtTelCel">Telefone Celular:</label></div>
<div>
<input type="text" id="txtTelCel" name="txtTelCel" size="50" maxlength="8">
</div>