How Can IntersectionObserver Enhance CSS3 Animations on Page Scroll?

Triggering CSS3 Animations on Page Scroll using IntersectionObserver API

When incorporating CSS3 animations into web pages, users may encounter challenges when the animations are triggered prematurely or not visible in the viewport. To address this issue, the IntersectionObserver API provides a solution that allows elements to be animated only when they enter the user's viewport.

IntersectionObserver API

The IntersectionObserver API enables developers to observe changes in the intersection of target elements with an ancestor element or the document viewport. This API provides a callback function invoked when the target element becomes visible or invisible.

Implementation

To implement this functionality:

1. Create an IntersectionObserver object with callback function inViewport to toggle a class on elements based on their visibility:

const inViewport = (entries, observer) => {
  entries.forEach(entry => {
    entry.target.classList.toggle("is-inViewport", entry.isIntersecting);
  });
};

const observer = new IntersectionObserver(inViewport);

2. Configure the intersection observer options as needed (e.g., root, rootMargin, threshold).
3. Observe target elements with data-inviewport attribute using the intersection observer:

document.querySelectorAll('[data-inviewport]').forEach(el => {
  observer.observe(el, obsOptions);
});

4. Implement CSS animations using class selectors:

[data-inviewport="fade-in"] {
  transition: 2s;
  opacity: 0;
}
[data-inviewport="fade-in"].is-inViewport {
  opacity: 1;
}

By following these steps, animations can be triggered dynamically based on an element's visibility in the viewport, providing a more intuitive and engaging user experience during page scrolling.

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