Intersection Observer API

The Intersection Observer API is a modern browser feature that allows developers to asynchronously observe changes in the intersection (i.e., visibility) of a target element with an ancestor element or the viewport. It’s a powerful tool for creating performant, scroll-aware functionality without relying on expensive scroll event listeners.

Common Use Cases:

• Lazy loading images or components only when they enter the viewport
  
  

• Infinite scrolling (e.g., loading more content as a user scrolls)
  
  

• Triggering animations or analytics tracking when elements come into view
  
  

• Sticky headers, parallax effects, and more

How It Works:

You create an observer that watches a DOM node and fires a callback when its visibility status changes.

const observer = new IntersectionObserver((entries) => {
  entries.forEach(entry => {
    if (entry.isIntersecting) {
      console.log('Element is in view');
    }
  });
});
observer.observe(document.querySelector('#myElement'));

Configuration Options:

root: The container to use as the viewport (defaults to the browser viewport)
threshold: A value from 0 to 1 that defines what percentage of the element is visible before triggering
rootMargin: Margin around the root (e.g., "0px 0px -100px 0px")

Why Intersection Observer Matters

Unlike traditional scroll-based logic, Intersection Observer is more performant, especially on mobile, because it runs asynchronously and is optimized by the browser. It avoids layout thrashing and reduces jank on scroll-heavy pages.

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