React

What is React and what problems does it solve?

How does React differ from a framework?

What is JSX and how does it work?

Why is the key prop needed in lists?

What is a component and what types of components are there?

What are props and how to use them correctly?

What is state and when is it needed?

How does useState work and why is setState asynchronous?

How to update objects and arrays in state without mutations?

What is derived state and why is it harmful?

What is lifting state up and when should you do it?

How does useEffect work and what is it used for?

How to correctly specify dependencies for useEffect?

What is the difference between useEffect and useLayoutEffect?

Why should hooks not be called conditionally?

What is useMemo and when is it useful?

What is useCallback and how does it differ from useMemo?

When does memo really help, and when does it not?

What is React.memo and how does it work?

Why is it dangerous to optimize React 'by eye'?

What is reconciliation in React?

What is virtual DOM and why is it not 'magic'?

Why does a component re-render and how to understand it?

What are controlled components (controlled forms)?

How to make uncontrolled input and when is it justified?

How to handle events correctly in React?

How does SyntheticEvent differ from native events?

How to work with refs properly and when are they needed?

What is forwardRef and when is it needed?

What is useImperativeHandle and should you use it?

What is the Context API and what are its limitations?

How to avoid unnecessary rerenders due to Context?

What are custom hooks and why are they needed?

How to design custom hooks to make them reusable?

What is React Router and what alternatives are there?

What are SSR, CSR, and SSG (in the context of React)?

What is hydration and what problems can occur?

Why does hydration mismatch happen and how to fix it?

How to safely use window/document in React?

How to work with data fetching in React?

How to properly handle loading/error/empty states?

How to cancel requests and avoid race conditions?

What is Suspense and what is it used for?

How does React.lazy and code splitting work?

What is Error Boundary and why is it needed?

How to create forms and validation in React?

What is React Hook Form and why is it popular?

How to implement debounce for search/input?

How to manage focus and accessibility (a11y) in React?

How to correctly implement a modal window?

What is a Portal and when is it needed?

How does batch updates work in React?

What is concurrent rendering in React 18?

What is useTransition and when is it useful?

What is useDeferredValue and how does it differ from debounce?

How to properly write keys and identifiers for components?

How to work with event handler lifting?

What is useReducer and when to choose it over useState?

How to design a reducer: actions and types?

How to avoid prop drilling?

What are children and how to use composition?

What are render props and when is it useful?

What are compound components and where are they used?

How to type props in React + TypeScript?

How to type components that accept a component/icon?

How to test React components?

What to test: unit, integration, or e2e?

How to mock fetch/HTTP requests in tests?

What is StrictMode and why can effects be called twice in dev?

How to properly log and debug React?

How to work with URL state (query params) in React?

How to store authorization tokens in a React app?

How to protect against XSS in React?

When to use dangerouslySetInnerHTML and how to do it more safely?

How to properly work with styles in React?

How to organize folders and architecture of a React project?

What is container/presentational pattern and is it still relevant?

How to avoid memory leaks in React?

Why can't you call setState after unmount and how to avoid it?