How would you test memo, useMemo, useCallback?

Answers use simple, clear English.

Quick interview answer

Test memo, useMemo, useCallback with unit checks for the happy path, integration tests for real I/O boundaries, and load/chaos checks so regressions show up before prod. Core idea: 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

Interview answer for testing memo, useMemo, useCallback: 1) Unit: isolate the pure logic behind memo, useMemo, useCallback with deterministic fixtures. 2) Integration: exercise real timers/I/O/network boundaries the way production does. 3) Load & soak: prove the event path still meets SLOs under concurrency. 4) Failure injection: break dependencies and assert recovery/backpressure. Best practices to include: Profile first; memo leaf components receiving stable props from unstable parents. Call out mistakes: Memoizing everything; useCallback with empty deps capturing changing state. Parent context: 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

Interviewers want a test strategy, not “I would write tests.” Tie each layer back to how memo, useMemo, useCallback fails: correctness, latency, and starvation. 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

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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