Top 10 React.js useMemo() Interview Questions

What is the useMemo() hook in React.js?

It memoizes a computed value to optimize performance by preventing unnecessary recalculations.

When should you use useMemo()?

Use it for expensive calculations or complex data transformations that don’t need to recompute on every render.

How does useMemo() differ from useCallback()?

useMemo() memoizes a value, while useCallback() memoizes a function.

What is the syntax of useMemo()?

const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);

What happens if you omit the dependency array in useMemo()?

The memoized value recomputes on every render, defeating its purpose.

Can useMemo() improve performance in all cases?

No, it’s only beneficial for computationally expensive operations; otherwise, it may add overhead.

What types of values can useMemo() return?

It can return any value: primitives, objects, arrays, or functions.

How does useMemo() handle dependency changes?

It recalculates the memoized value only when dependencies change.

Can useMemo() be used to memoize JSX elements?

Yes, but it’s rare; use it for JSX when rendering is expensive and props are stable.

What’s a common mistake when using useMemo()?

Overusing it for simple calculations, which can lead to unnecessary complexity and overhead.