make simple scroll function with vanilla js

js-scroll.js

<script type="text/javascript">
   function slide(src,nome){
     document.getElementById(nome).removeAttribute('style');
     document.getElementById(nome).setAttribute('style','background-image:url('+src+')');
   }
   
   function next (id,project) {
   var width=document.getElementById(project).offsetWidth;
   var container = document.getElementById(id);
   sideScroll(container,'right',18,width,10);
   };
   
   function back(id,project) {
   var width=document.getElementById(project).offsetWidth;
   var container = document.getElementById(id);
   sideScroll(container,'left',18,width,10);
   };
   
   function sideScroll(element,direction,speed,distance,step){
   scrollAmount = 0;
   var slideTimer = setInterval(function(){
       if(direction == 'left'){
           element.scrollLeft -= step;
       } else {
           element.scrollLeft += step;
       }
       scrollAmount += step;
       if(scrollAmount > distance){
           window.clearInterval(slideTimer);
       }
   }, speed);
   }
   
   function openNav(nav) {
   document.getElementById(nav).style.width = "100%";
   }
   
   function closeNav(nav) {
   document.getElementById(nav).style.width = "0%";
   }
   
</script>