Question 1

What is rootMargin in lazy loading?

Accepted Answer

RootMargin expands or shrinks the viewport bounding box before triggering load. Positive values start loading earlier (preload), negative values delay loading.

Question 2

How does IntersectionObserver compare to native loading=lazy?

Accepted Answer

IntersectionObserver offers custom rootMargin and thresholds, while native loading=lazy is simpler but less flexible. Both defer offscreen resources.

Question 3

What bandwidth savings can I expect?

Accepted Answer

Savings depend on viewport size, page height, and resource positions. Typically 30-70% of image weight can be deferred for bounce visitors.