Lazy Loading Explained

You open a long page with forty images, a chat widget, an analytics script, and a video player near the bottom - if the browser fetched all of it the instant you arrived, you'd wait for things you might never scroll to. Lazy loading is the fix: don't do the work until something proves it's needed. This guide covers the idea, the three places you'll use it constantly, and the tradeoff that keeps it from being a free lunch.

How to read this

Phase 1 builds the mental model - the difference between eager and lazy, and why "load everything now" is the default that quietly costs you. Phase 2 is where you'll actually use it day to day: images, route-based code, and "load more" patterns. Phase 3 is the clear-eyed tradeoff - what lazy loading can break, and when loading eagerly is the better call.

The phases

1. Don't do work nobody asked for yet - the general principle, contrasted with eager loading.
2. Where you'll actually use it - images, code-splitting, and infinite scroll.
3. The tradeoff - layout shift, missing content, and when eager wins.