React.js

Components, hooks, virtual DOM, reconciliation, state management, and performance.

81 questions across 38 sections

Brief Interview Examples

5 questions

Basic Concepts

4 questions

JSX

4 questions

Components

2 questions

Props

3 questions

State

3 questions

State vs Props

3 questions

Virtual DOM

3 questions

Reconciliation

2 questions

React Fiber

3 questions

Rendering

2 questions

Keys

3 questions

Conditional Rendering

1 questions

Lists

1 questions

Fragments

2 questions

React Hooks

3 questions

useEffect()

4 questions

useMemo()

2 questions

useCallback()

1 questions

React.memo()

1 questions

useRef()

2 questions

useContext()

2 questions

Custom Hooks

2 questions

Rules of Hooks

1 questions

Controlled Components

1 questions

Forms

1 questions

Lifting State Up

1 questions

Composition

1 questions

Error Boundaries

2 questions

Portals

2 questions

Lazy Loading

1 questions

Suspense

1 questions

Code Splitting

1 questions

State Management

4 questions

Redux Toolkit

2 questions

RTK Query

1 questions

React Query (TanStack Query)

1 questions

React Performance

3 questions

Security

Next.js

Brief Interview Examples

Explain React state with a simple example.

Explain props with a simple example.

Explain useEffect with a practical example.

Explain React keys with a proper example.

Explain controlled components with a form example.

Basic Concepts

What is React?

Why use React?

Advantages of React.

Why is React called a library instead of a framework?

JSX

What is JSX?

Can browsers understand JSX directly?

What happens after writing JSX?

Why can JSX contain JavaScript?

Components

Difference between Functional and Class Components.

Why are Functional Components preferred today?

Props

What are Props?

Can Props be modified?

Difference between Props and State.

State

What is State?

When should State be used?

Difference between State and Variables.

State vs Props

Difference between Props and State.

Which one is immutable?

Can child components modify Props?

Virtual DOM

What is Virtual DOM?

Why is Virtual DOM faster?

Does React always update the entire DOM?

Reconciliation

What is Reconciliation?

How does React compare two Virtual DOM trees?

React Fiber

What is React Fiber?

Why was Fiber introduced?

Difference between old React and Fiber.

Rendering

What triggers Re-render?

Does every state update re-render the whole application?

Keys

Why are Keys important?

Can index be used as Key?

Why is using index as Key discouraged?

Conditional Rendering

Different ways to render conditionally.

Lists

How do you render lists?

Fragments

Why use Fragments?

Difference between div and Fragment.

React Hooks

How does useState work?

Can State updates be asynchronous?

Why use functional updates?

useEffect()

What is useEffect?

When does it execute?

Difference between useEffect(), useEffect([]), and useEffect([count])?

Why return a function inside useEffect?

useMemo()

What is useMemo?

When should useMemo be used?

useCallback()

Difference between useMemo and useCallback.

React.memo()

Difference between React.memo(), useMemo(), and useCallback().

useRef()

What is useRef?

Difference between useRef and useState.

useContext()

What problem does Context API solve?

When should Context not be used?

Custom Hooks

What is a Custom Hook?