| 1 | What is the difference between useEffect and code that runs directly during rendering? React › Effects & Lifecycle | React | Effects & Lifecycle | Beginner |
| 2 | How would you fetch data safely inside useEffect while avoiding a common bug called a race condition? React › Effects & Lifecycle | React | Effects & Lifecycle | Advanced |
| 3 | What is the useEffect hook used for in React? React › Effects & Lifecycle | React | Effects & Lifecycle | Beginner |
| 4 | What does the dependency array in useEffect actually control? React › Effects & Lifecycle | React | Effects & Lifecycle | Intermediate |
| 5 | How do you clean up an effect in React, and why is it important? React › Effects & Lifecycle | React | Effects & Lifecycle | Intermediate |
| 6 | What does componentDidMount do in a class component and what is its equivalent using hooks? React › Class Components & Legacy Lifecycle Methods | React | Class Components & Legacy Lifecycle Methods | Intermediate |
| 7 | What is componentDidUpdate used for, and what mistake should you watch out for when using it? React › Class Components & Legacy Lifecycle Methods | React | Class Components & Legacy Lifecycle Methods | Advanced |
| 8 | Why does Strict Mode call component functions and certain effects twice during development? React › Strict Mode & Concurrent Features | React | Strict Mode & Concurrent Features | Intermediate |
| 9 | What is a custom hook in React and why would you create one? React › Custom Hooks | React | Custom Hooks | Beginner |
| 10 | What problem do libraries like React Query and SWR solve compared to fetching data with plain useEffect? React › Data Fetching (React Query & SWR) | React | Data Fetching (React Query & SWR) | Beginner |
| 11 | Why is it usually better to use a data fetching library instead of writing your own fetch logic in every component? React › Data Fetching (React Query & SWR) | React | Data Fetching (React Query & SWR) | Beginner |
| 12 | What does the useState hook do, and how do you use it? React › Hooks | React | Hooks | Beginner |
| 13 | What is a ref in React and what is it used for? React › Refs, useRef & forwardRef | React | Refs, useRef & forwardRef | Beginner |
| 14 | What is React Strict Mode and what does it actually do? React › Strict Mode & Concurrent Features | React | Strict Mode & Concurrent Features | Beginner |
| 15 | What is useLayoutEffect and how is it different from the regular useEffect hook? React › Concurrent Hooks (useTransition, useDeferredValue & useLayoutEffect) | React | Concurrent Hooks (useTransition, useDeferredValue & useLayoutEffect) | Intermediate |
| 16 | How would you write a custom hook to fetch data from an API and share that logic across components? React › Custom Hooks | React | Custom Hooks | Intermediate |
| 17 | Why does React not catch errors that happen inside event handlers, like an onClick function, using error boundaries? React › Error Boundaries | React | Error Boundaries | Intermediate |
| 18 | What is the useMemo hook and how does it help with performance? React › Hooks | React | Hooks | Intermediate |
| 19 | How is useRef different from useState when it comes to storing a value? React › Refs, useRef & forwardRef | React | Refs, useRef & forwardRef | Intermediate |
| 20 | How would you use a ref to keep track of a component's previous prop value? React › Refs, useRef & forwardRef | React | Refs, useRef & forwardRef | Intermediate |
| 21 | What is hydration mismatch, and what commonly causes this error in a React app using server rendering? React › Static Site Generation (SSG) & Hydration | React | Static Site Generation (SSG) & Hydration | Intermediate |
| 22 | How would you test a component that fetches data when it first appears on the screen? React › Testing | React | Testing | Intermediate |
| 23 | How does React's reconciliation process handle components of a completely different type appearing in the same position? React › Virtual DOM & Reconciliation | React | Virtual DOM & Reconciliation | Intermediate |
| 24 | How would you manage focus properly in a React modal to keep it accessible? React › Accessibility (a11y) in React | React | Accessibility (a11y) in React | Advanced |
| 25 | How would you build a custom hook that debounces a fast changing value, such as text typed into a search box? React › Custom Hooks | React | Custom Hooks | Advanced |
| 26 | How would you use React DevTools to find out why a component re rendered when you did not expect it to? React › React DevTools & Debugging | React | React DevTools & Debugging | Advanced |