import-on-visibility

Lazy loading React components on viewport entry uses IntersectionObserver to detect visibility and dynamically import the module, rendering a fallback UI during the load-to-render transition to improve web performance.

Deferring JavaScript module imports for below-the-fold widgets requires registering an on-visibility trigger with IntersectionObserver, dynamically importing the target module, and showing a lightweight placeholder until rendering completes.

Lazy loading with IntersectionObserver works for client-side apps by delaying heavy component imports until elements enter the viewport, preventing unnecessary work during the first render and improving perceived performance.

Dynamic importing on visibility improves web performance by deferring JavaScript imports for components not immediately visible, preventing unnecessary parsing and compilation work during the first render.

You can show a loading fallback while dynamically importing a module on viewport entry by rendering a lightweight placeholder during the fetch, parse, compile, and execute phases of the deferred component.

Viewport-based lazy loading should not be used for above-the-fold components that users need immediately, as the dynamic import delay and fallback rendering transition can degrade perceived performance.