JS - React Questions
1/12/2025 • FULLSTACK
Table of Contents
JavaScript and React Important Topics
JavaScript
Famous JavaScript Interview Topics
- Closures: Understanding how closures work and their use cases.
- Promises and Asynchronous Programming: Working with Promise, async/await, and handling asynchronous operations.
- Event Loop and Callbacks: Knowledge of how the event loop works and managing callbacks in JavaScript.
- Hoisting, Scope, and Execution Context: How variables and functions are hoisted, and the difference between function scope and block scope.
- Prototypes and Inheritance: Understanding prototype chain, inheritance patterns, and the
thiskeyword. - Event Delegation: Efficient event handling through event delegation and understanding the event propagation mechanism.
- Debouncing and Throttling: Techniques for optimizing performance, particularly with input handling and scrolling events.
- JavaScript Data Structures: Understanding arrays, objects, maps, sets, and working with higher-order functions like
map,filter,reduce. - Functional Programming Concepts: Principles of functional programming, including immutability, pure functions, and higher-order functions.
- Error Handling: Properly handling errors using
try/catch, and understanding custom error creation.
Famous JavaScript Interview Questions
- What is the difference between
==and===? - Explain closures in JavaScript.
- How does prototypal inheritance work?
- What is the event loop in JavaScript?
- Explain the concept of hoisting.
- What are the differences between
var,let, andconst? - How does the
thiskeyword work in JavaScript? - What is the purpose of the
use strictdirective? - Explain the difference between synchronous and asynchronous code in JavaScript.
- What are Promises and how do they work?
- How does the
async/awaitsyntax work? - What is the difference between
nullandundefined? - Explain the concept of callback functions.
- What is the difference between
forEach()andmap()? - How do you handle errors in JavaScript?
- What is the purpose of the
bind()method? - Explain the concept of event bubbling and capturing.
- What is memoization and how can it be implemented in JavaScript?
- How does JavaScript handle asynchronous programming?
- What are arrow functions and how do they differ from regular functions?
- Explain the concept of debouncing and throttling.
- What is the difference between
Object.create()and the constructor pattern? - How does the module pattern work in JavaScript?
- What are generator functions and how are they used?
- Explain the concept of currying in JavaScript.
- How does the
setTimeout()function work? - What is the purpose of the
Array.prototype.reduce()method? - How do you clone an object in JavaScript?
- What is the difference between
call(),apply(), andbind()? - Explain the concept of lexical scope in JavaScript.
React
Important React Topics
- Component Lifecycle: Understanding the lifecycle of class components, including methods like
componentDidMount,shouldComponentUpdate, andcomponentWillUnmount. - Hooks (
useState,useEffect,useContext, etc.): Mastery of React hooks, including custom hooks, and their use cases. - State Management: Managing state within components, lifting state up, and using state management libraries like Redux or Context API.
- Component Composition and Reusability: Best practices for composing and reusing components, and understanding props and prop drilling.
- Virtual DOM and Reconciliation: Understanding how React’s virtual DOM works and the reconciliation process.
- React Router: Handling client-side routing with React Router, including nested routes and dynamic parameters.
- Handling Side Effects: Managing side effects in React using
useEffectand libraries like Redux Thunk or Redux Saga. - Optimizing Performance: Techniques for optimizing performance in React apps, including memoization (
React.memo,useMemo,useCallback). - Testing React Components: Writing unit tests for React components using testing libraries like Jest and React Testing Library.
- Forms and Controlled Components: Handling forms, managing controlled and uncontrolled components, and form validation.
Famous React Interview Questions
- What is React and what are its main features?
- Explain the difference between functional and class components.
- What is JSX?
- What are props in React?
- Explain the concept of state in React.
- What is the virtual DOM and how does it work?
- What are React hooks? Name a few commonly used hooks.
- Explain the lifecycle methods in class components.
- How do you handle events in React?
- What is the significance of keys in React lists?
- What is the purpose of
React.Fragment? - Explain the concept of conditional rendering in React.
- What is the difference between controlled and uncontrolled components?
- How do you pass data between components in React?
- What is context in React and when would you use it?
- Explain the concept of higher-order components (HOCs).
- What is the purpose of the
useEffecthook? - How do you optimize performance in a React application?
- What is code-splitting in React and why is it useful?
- Explain the concept of lifting state up.
- What are error boundaries in React?
- How does React handle forms?
- What is the difference between Element and Component in React?
- Explain the concept of reconciliation in React.
- What are pure components in React?
- How do you implement server-side rendering with React?
- What is the significance of the key prop when rendering lists?
- How do you handle routing in a React application?
- What are React portals and when would you use them?
- Explain the concept of React Suspense and lazy loading.
Resources for Practice
30DaysCoding
Frontend Interview Preparation
JavaScript Projects with ChatGPT
- Todo List App
- Weather app with real-time data
- Simple calculator
- Signature app with canvas
- BMI calculator
React Projects with ChatGPT
- Weather App
- RSS API App
- Finance Trading App
- Fitness Tracking App