Question 1

What are React Hooks? Name a few common ones.

Accepted Answer

**Target Audience:** Anyone preparing for a React interview — assumes components and props. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The hook inventory in section 4 was read directly off the installed React 19.2.8 rather than recalled, which matters because several were added recently. ## 1. Why This Even Matters — A Story First Imagine a workshop where only the master craftsmen were allo

Question 2

How do you handle side effects in functional components?

Accepted Answer

**Target Audience:** Frontend engineers preparing for React interviews — assumes basic familiarity with Hooks. **Difficulty:** Medium > **How to read this doc:** Every concept is explained in plain language first, then tagged with 📌 Interview term: — the exact vocabulary an interviewer expects. Every ordering and lifecycle claim below was produced by actually running React 19.2.8 in a real DOM (jsdom) in this repo, not described from documentation. ## 1. Why This Even Matters — A

Question 3

What is the purpose of the cleanup function in useEffect?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useEffect basics. **Difficulty:** Easy to Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The exact call sequence in section 3 was produced by rendering a component through three dependency changes and an unmount on React 19.2.8. ## 1. Why This Even Matters — A Story First Every time you check into a hotel you get a key. Ever

Question 4

What are React's design principles?

Accepted Answer

**Target Audience:** Engineers preparing for senior React interviews — assumes broad familiarity with the API. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This is a discussion question rather than a mechanical one, so instead of a "Verified" section it cites the React team own published principles and ties each to a concrete API you already use. ## 1. Why This Even Matters — A Story First

Question 5

What is the purpose of the `deps` array in `useEffect` and `useCallback`?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useEffect basics. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every count in sections 3 and 5 was measured by rendering the components three times on React 19.2.8 and recording how often each hook actually ran. ## 1. Why This Even Matters — A Story First A courier is told: "redeliver whenever the address c

Question 6

Describe the React component lifecycle.

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes hooks basics. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every ordering below is **executed output from React 19.2.8**, not a description — the raw sequences are in sections 3 and 5. ## 1. Why This Even Matters — A Story First A market stall has three moments: setting up before opening, adjusting through the day as st

Question 7

How do you handle asynchronous operations in React functional components?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useEffect and promises. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The race-condition outcome in section 4 and React warning text in section 3 were both produced by running the code on React 19.2.8, not described from memory. ## 1. Why This Even Matters — A Story First You order a taxi, change your mind,

Question 8

How do you fetch data in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useEffect. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This doc is the decision landscape; async operations covers the mechanics and race conditions, and

Question 9

How do you interact with external APIs in React?

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes fetch and hooks. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. This doc is about **integration architecture**; how to fetch data in React covers choosing a fetching strategy, and

Question 10

Explain the purpose of `useEffect`.

Accepted Answer

**Target Audience:** Engineers preparing for React interviews — assumes useState. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. The render counts in section 4 were measured on React 19.2.8. This doc focuses on *when an effect is the wrong tool*; see handling side effects for the broader strategy an

REACT.JSDECODED.

Easy

What are React Hooks? Name a few common ones.

How do you handle side effects in functional components?

What is the purpose of the cleanup function in useEffect?

Medium

What are React's design principles?

What is the purpose of the `deps` array in `useEffect` and `useCallback`?

Describe the React component lifecycle.

How do you handle asynchronous operations in React functional components?

How do you fetch data in React?

How do you interact with external APIs in React?

Explain the purpose of `useEffect`.

Async Server Components & waterfall prevention — fetching without blocking

Hard

What causes stale closures in React hooks, and how do you fix them correctly?

What are Effect Events (`useEffectEvent`) and what problem do they solve?

useEffectEvent — separating reactive and non-reactive logic in Effects

What underlying mechanism makes the Rules of Hooks mandatory?

When would you use `useLayoutEffect` instead of `useEffect`?

What can and can't an Error Boundary catch?