Si es para numeros enteros (no decimales)
Código HTML:
Ver original<!DOCTYPE html>
<script type="text/javascript"> //<![CDATA[
function validar(e){
var expresion=/[\d]/;
if(expresion.test(String.fromCharCode(e.which))){
return expresion.test(String.fromCharCode(e.which));
}else{
alert('error');
return false;
}
}
//]]>
<input type="text" id="numero" name="numero" onkeypress="return validar(event)" />
Saludos)