function count_chars()
{
    var counter = document.forms['room_form'].extrainf.value;
    var lengte = parseInt(counter.length);
    
    if(lengte > 800)
    {
        window.alert('You have reached the maximum of characters allowed!');
        teller = counter.substr(0, 800);
        
        document.forms['room_form'].extrainf.value = counter;
        return;
    }
        document.getElementById('characters').innerHTML = lengte;
}