Light scroll animation on pure JS. Code example

 // Scroll animations
  function onEntry(entry) {
    entry.forEach(change => {
      if (change.isIntersecting) {
        change.target.classList.add('element-show');
      }
    });
  }

  let options = {
    threshold: [0.5]
  };
  let observer = new IntersectionObserver(onEntry, options);
  let elements = document.querySelectorAll('.element-animation');

  for (let elm of elements) {
    observer.observe(elm);
  }

IF you want remove .element-show class after element leaving the viewport

document.addEventListener('DOMContentLoaded', () => {
    if (document.querySelector('.element-animation')) {
        function onEntry(entry) {
            entry.forEach(change => {
                if (change.isIntersecting) {
                    change.target.classList.add("element-show");
                } else {
                    change.target.classList.remove("element-show");
                }
            });
        }

        let options = {
            threshold: [0.5]
        };
        let observer = new IntersectionObserver(onEntry, options);
        let elements = document.querySelectorAll(".element-animation");

        for (let elm of elements) {
            observer.observe(elm);
        }
    }
});