window.onload = function(){

 var bannerlr = document.getElementById('banner-lr');

 var lest = document.getElementById('bann-ul');

 var buttons = document.getElementById('buttons').getElementsByTagName('span');

 var next = document.getElementById('banner-an');

 var part = document.getElementById('banner-anr');

 var index = 1;

 function show(){

 buttons[index - 1].className = 'on';

 }

 function animate(offset){

    var newleft = parseInt(lest.style.left)+offset

    lest.style.left = newleft+ 'px';

 if(newleft < -8130){

 lest.style.left = -450 + 'px';

  }

  if(newleft > -450){

  lest.style.left = -8130 + 'px';

}

    }

         next.onclick = function(){

index += 1;

show(); 

        animate(-1920)

        };

         part.onclick = function(){

 index -=1;

 show();

            animate(1920)

        }

 }