const targets = document.getElementsByClassName('fade');
for(let i = targets.length; i--;){
 let observer = new IntersectionObserver((entries, observer) => {
  for(let j = entries.length; j--;){
   if (entries[j].isIntersecting) {
    entries[j].target.classList.add('active');
   } else{
    entries[j].target.classList.remove('active');
   }
  }
 });
 observer.observe(targets[i]);
}