Describe a situation where a performance issue in a Next.js dashboard (e.g., slow page loads, janky charts, or heavy data tables) impacted users. How did you identify the root cause and what specific optimizations did you implement?

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VirtualInterview.AI · Accepted Answer

On a customer analytics dashboard I owned, support started getting complaints that the “Accounts” page froze for 3–5 seconds when filtering large datasets. This page was key for about 150 account managers, so it was pretty visible. I profiled it using Chrome DevTools and Next’s bundle analyzer and saw two main issues: a 600kb charting library loading on every interaction, and a giant table doing expensive calculations on the client.

I tackled it in layers. First, I code‑split the charts with dynamic imports and disabled SSR for them, which cut the main bundle by ~30%. Then I pushed most of the aggregation logic to an API route, returning pre‑computed rows, and added pagination + virtualized rendering with React Window. Finally, I memoized some heavy components and normalized state.

The result was a drop in interaction latency from ~3s to under 300ms and a 40% reduction in time‑to‑interactive. Support tickets about “frozen pages” went to zero the following month.

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