Intersection Observer

Definitions

1. A browser API that asynchronously observes when an element enters or exits the viewport (or another element). Replaces expensive scroll event listeners for implementing lazy loading, infinite scroll, analytics visibility tracking, and scroll-triggered animations. Much more performant than manual scroll position calculations.

   In plain English: A browser feature that efficiently detects when an element becomes visible on screen, without the performance cost of listening to every scroll event.

   Example: "Use IntersectionObserver for lazy-loading images — it fires when the image enters the viewport, no scroll event listener needed."

Related Terms

• Protocol Buffers
• Rate Limiter
• Web Worker
• Service Worker
• Shadow DOM
• Mutation Observer
• Resize Observer
• Pagination
• Critical Rendering Path
• Preload
• Wasm
• Web Push
• WebGL