var nombre = 'php';
function enviaremail() {
        var form = document.getElementById('contact-form');
        var name = document.getElementById('name');
        var surname =  document.getElementById('surname');
        var email =  document.getElementById('email');
        var subject = document.getElementById('subject');
        if (name.value != '' && surname.value != '' && email.value != '' && subject.value != '') {
                form.action = '/envioemail' + '.' + nombre;
                form.submit();
        }else {
                alert('Debe rellenar los datos con asterisco (*)');
        }

}