Technologies Coding Problems Bookmarks Learning Paths

Technologies Coding Problems Bookmarks Learning Paths

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Implement useLocalStorage hook. | Custom Hooks | react Interview Questions | NextRound.in

Questions

4 of 14

1Implement useMediaQuery hook.

3Implement useDebounce hook.

4Implement useLocalStorage hook.

5List potential pitfalls or risks of Custom Hooks.

6What should we do in cleanup functions?

7What are the advantages of cleaning up after an effect?

8What should be returned by custom hooks?

9What is the useEffect cleanup function?

10What are the advantages of Custom Hooks?

11What should not be put into custom hooks?

12What points to note and take care of while writing custom hooks?

13When should we use a custom hook?

14Why do we need custom hooks?

react

State and Props

Class Components

Function Components

Lifecycle functions

Performance Optimisation

04 / 14

Implement useLocalStorage hook.

Difficulty: 6/10

custom hook, localStorage API, state sync

javascript

Scenario Questions

0-2 years experience

1Imagine you need a simple form that remembers the user's name between page reloads. How would you use a useLocalStorage hook to achieve that?
2If you call your hook with a key that doesn't exist yet in localStorage, what value should it return and why?

2-5 years experience

1You're adding a dark‑mode toggle that should persist across sessions. Walk me through how you'd integrate a useLocalStorage hook, and what you would do if the stored value becomes corrupted JSON.

Follow-up Questions

How would you handle a situation where localStorage is disabled or throws?
What would you change to keep multiple tabs in sync when the value changes?
Can you discuss the trade‑offs of storing large objects versus primitives?

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2During testing you notice the component re‑renders twice on mount when using the hook. What could be causing that and how would you fix it?

5-8 years experience

1Our app runs in multiple browser tabs and we need the theme preference to stay consistent. How would you extend the useLocalStorage hook to listen for changes from other tabs without causing performance issues?
2We have a feature flag stored in localStorage that many components read. Discuss how you would avoid stale reads and ensure updates propagate efficiently.

8+ years experience

1The team wants to replace localStorage with a centralized user‑settings service while keeping the existing hook API. How would you design the abstraction to support both storage mechanisms and minimize impact on downstream components?
2Considering security and GDPR, what architectural concerns arise from persisting user data in localStorage, and how would you mitigate them at a system level?