intermediate
Frontend performance
Browser and application techniques that improve loading, rendering, responsiveness, and interaction quality for real users.
Frontend performance interviews focus on what real users feel: loading, interactivity, and visual stability—not Lighthouse scores in isolation. FullStack JS teams ship React/Next apps where bundle size, code splitting, images, caching, and list virtualization directly affect conversion and SEO.
Subtopics: Core Web Vitals, bundle size, code splitting, lazy loading, image optimization, caching, virtualization.
On interviews: prioritize LCP element, explain INP vs old FID, prevent CLS from late fonts or images, and tie improvements to field data (CrUX/RUM).
Common pitfalls: lazy-loading the hero image; splitting so aggressively that waterfalls multiply; caching personalized HTML; virtualizing without keyboard focus.
The trade-off is faster first paint versus complexity of loading strategy and cache correctness.
Checklist:
- Measure field data on critical routes.
- Budget JS and CSS per route.
- Reserve space for media and fonts.
- Validate on mid-tier mobile networks.