Tell me about a recent task you struggled with — one that initially seemed simple but turned out to be complex.

Once, it was necessary to implement a simple animation of elements appearing on the page during scrolling. At first, it seemed enough to add a CSS animation and listen to the scroll event to trigger the animation. However, in practice, there were performance issues and incorrect triggering during fast scrolling.

It was necessary to delve deeper into the Intersection Observer API, which allows efficient tracking of elements entering the viewport without constant scroll event handlers. This solution significantly improved responsiveness and reduced the load on the browser.

Example of using Intersection Observer:

const observer = new IntersectionObserver((entries) => {
  entries.forEach(entry => {
    if (entry.isIntersecting) {
      entry.target.classList.add('animate');
      observer.unobserve(entry.target); // to ensure the animation runs only once
    }
  });
});

document.querySelectorAll('.animate-on-scroll').forEach(el => {
  observer.observe(el);
});

Thus, a task that seemed simple required learning new APIs and optimizing the approach.