What metrics prove memo, useMemo, useCallback is healthy in prod?

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Quick interview answer

Prove memo, useMemo, useCallback is healthy with latency (p50/p95/p99), error/saturation rates, and queue/event-loop lag — not just CPU. Context: Logic: React.memo skips re-render if props shallow-equal. useMemo caches computed value; useCallback caches function reference — helps memoized children avoid redundant renders.

Detailed answer

Production health signals for memo, useMemo, useCallback: • Latency: p50/p95/p99 of the critical path that uses memo, useMemo, useCallback. • Errors: failure rate, timeouts, and retry storms. • Saturation: queue depth, event-loop delay, thread/pool utilization. • Business SLIs: request success and user-visible freshness where relevant. Trade-off lens: Pros: Targets expensive subtrees without manual shouldComponentUpdate. Cons: Premature optimization — memo has comparison cost; stale closures if deps wrong. Explain thresholds + alerts, then how you triage. Parent context: Logic: React.memo skips re-render if props shallow-equal. useMemo caches computed value; useCallback caches function reference — helps memoized children avoid redundant renders.

Full explanation

Good answers name measurable signals and what “bad” looks like for memo, useMemo, useCallback. React.memo skips re-render if props shallow-equal. useMemo caches computed value; useCallback caches function reference — helps memoized children avoid redundant renders.

Follow-up questions

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Parent context — memo, useMemo, useCallback

Logic: React.memo skips re-render if props shallow-equal. useMemo caches computed value; useCallback caches function reference — helps memoized children avoid redundant renders.

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