Top 3 Rendering Interview Questions
Browse 3 real-world technical and behavioral interview questions about Rendering. Review scenarios, edge cases, and architectural best practices.
Someone added will-change: transform to every card to make scrolling smooth, and the page got slower on phones. What happened?
Each will-change: transform requests its own compositor layer, a raster in memory sized by area and device pixel ratio. Hundreds of idle layers exhaust a phone's GPU memory and add compositing work, and scrolling was never limited by the cards. Remove the blanket rule, find the real jank, promote only what animates.
A page has a poor Largest Contentful Paint. How do you diagnose it and what do you actually change?
Split the LCP into TTFB, resource load delay, resource load time and render delay, use field attribution rather than a single lab run to see which part dominates, then fix that part specifically - prioritise the hero image, stop lazy-loading it, and remove render-blocking work.
Why is animating transform cheaper than animating top, and when does promoting an element to its own compositor layer make things worse?
Transform and opacity can be applied by the compositor to an already-rasterised layer, skipping style, layout and paint, and running off the main thread. Promotion buys that at the cost of memory, extra rasterisation and layers you forgot to retire.