Intersection Observer API là gì?

API async theo dõi khi element xuất hiện/biến mất khỏi viewport.

• Thay thế scroll event listener (tốn performance).
• Dùng cho lazy loading images, infinite scroll, trigger animations khi element visible.

An async API that watches when an element enters or leaves the viewport.

• Replaces scroll event listeners (which are expensive on performance).
• Used for lazy loading images, infinite scroll, and triggering animations when elements become visible.