
<!---------------------------------->
<script language="javascript">
function valida(c)
{
var i,v;
if(c)
{
i=c.name+"obl";
(c.value.length<=0)?v="visible":v="hidden";
document.getElementById(i).style.visibility=v;
}
}
</script>
<form>
email:
<input type="text" name="email" onBlur="valida(this);">
<span id="emailobl" style="visibility:hidden;"><b>El campo 'email' es obligatorio</b></span>
nombre:
<input type="text" name="nombre" onBlur="valida(this);">
<span id="nombreobl" style="visibility:hidden;"><b>El campo 'nombre' es obligatorio</b></span><p>
<select name="combo" onChange="submit()">
<option>Seleccion</option>
<option value="1">a</option>
<option value="2">b</option>
<option value="3">c</option>
</select>
</form>