How to filter the result of an ajax request?

I have a small ajax code that brings a value from the server, but when I want to use the result in the html the whole header is printed again.

<SCRIPT>
$("#proveedor").change(function(){
    $.ajax({
        url: "/producto/cantidadDeProductos/1", 
        success: function(res){
            alert(res);
        }
    });
});
</SCRIPT>