var scrolling = null; 
  
    function scroll_up() { 
        var d = document.getElementById('scroller'); 
  
        d.scrollTop = d.scrollTop - 20; 
  
        scrolling = window.setTimeout(function() { 
            scroll_up(); 
        }, 80); 
    } 
  
    function scroll_down() { 
        var d = document.getElementById('scroller'); 
  
        d.scrollTop = d.scrollTop + 20; 
  
        scrolling = window.setTimeout(function() { 
            scroll_down(); 
        }, 80); 
    } 
  
    function stop_scroll() { 
        window.clearTimeout(scrolling); 
}