In short
An efficient browser API for detecting when an element enters or leaves the viewport — powers lazy-loading, infinite scroll and scroll-triggered animations without expensive scroll listeners. It lets the browser efficiently determine visibility relationships without repeatedly calculating element positions inside high-frequency scroll handlers.
How to learn this
- 1Use it to lazy-load images only as they scroll into view. Verify the behavior with realistic data and handle the failure or empty state as well.
- 2Build a simple 'fade in on scroll' effect for page sections. Keep the first version small, then add one improvement after the core behavior works.
- 3Learn `threshold` and `rootMargin` options for fine-tuning when it triggers.
More topics at this stop
Stuck on this topic? Ask an Insider
Get 1:1 guidance from people who've walked this exact path — on the InsideEdge app.
