Top 100 React JS Interview Questions and Answers

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React Basics-1
Q1 3:08 what us React? What is the Role of React in software development?
Q2 6:15 what are the key Features of React?
Q3 8:00 what is DOM? What is the difference between HTML
& DOM?
Q4 10:59 What is virtual DOM ? Difference between DOM &
Virtual DOM?
Q5 15:36 What are React Components? What are the main
elements of it?
Q6 17:25 What is SPA (Single Page Application)?
Q7 19:10 What are the 5 advantages of React?
Q8 21:41 What are the disadvantages of React?
Q9 22:56 What is the role of JSX in React?
Q10 25:01 what is the difference between Declarative &
Imperative Syntax?
React Basics-2 26:52
Q11 27:33 What is Arrow Function Expression in JSX?
Q12 30:17 How to Setup React first project?
Q13 32:40 What are the Main files in React project?
Q14 34:57 How React app Load & display the components in
browser?
Q15 36:37 What is the difference between React & Angular?
Q16 39:38 What are the other 5 JS frameworks other than
React?
Q17 40:18 Whether React is Framework or Library? what is
the difference?
Q18 41:45 How React provide Reusability & Composition?
Q19 43:59 What are State, Stateless, Stateful and state
management teams?
Q20 47:05 What are Props in JSX?
React Basics-3 48:05
Q21 48:58 What is NPM? What is the role of node_module
folder?
Q22 50:26 What is the role of public folder in React?
Q23 51:29 What is the role of src folder in React?
Q24 52:12 What is the role of index.html page in React?
Q25 53:22 What is the role of index.js file & ReactDOM in
React?
Q26 55:28 What is the role of App.js file in React?
Q27 56:52 What is the role of function & return inside
App.js?
Q28 58:43 Can we have function without a return inside
App.js?
Q29 1:00:28 What is the role of export default inside
App.js?
Q30 1:01:25 Does the file name & component name must be
same in React?
React -4 JSX - 1:02:04
Q31 1:02:48 What is the role of JSX in React?
Q32 1:04:56 What are the 5 Advantages of JSX?
Q33 1:07:15 What is Babel?
Q34 1:08:29 What is the role of Fragment in JSX?
Q35 1:10:35 What is Spread Operator in JSX?
Q36 1:11:55 What are the types of Conditional Rendering
in JSX?
Q37 1:14:50 How do you iterate over a list in JSX? What
is map() method?
Q38 1:17:39 Can a browser read a JSX file?
Q39 1:18:01 What is Transpiler? What is the difference
between Compiler & Transpiler?
Q40 1:19:26 Is it possible to use JSX without React?
React- 5 Components-Functional/Class 1:19:57
Q41 1:20:47 What are React Components ? what are the main
elements of it?
Q42 1:22:38 What are the Types of React Components? What
are Functional Components?
Q43 1:23:41 How do you pass data between functional
components in React?
Q44 1:23:58 What is Prop Drilling in React?
Q45 1:25:06 Why to Avoid Prop Drilling? In how many ways
avoid Prop Drilling?
Q46 1:27:36 What are class components in React?
Q47 1:29:18 How to pass data between class components in
React?
Q48 1:30:30 What is the role of this keyword in class
components?
Q49 1:32:05 What are the 5 differences btw Functional
components & class components?
React- 6 Routing 1:34:09
Q50 1:34:43 What is Routing and Router in React?
Q51 1:36:02 How to implement Routing in React?
Q52 1:37:47 What are the roles of <Routes> & <Route>
component in React Routing?
Q53 1:39:12 What are Route Parameters in React Routing?
Q54 1:39:52 What is the role of Switch Component in React
Routing?
Q55 1:41:05 What is the role of exact prop in React
Routing?
React- 7 Hooks -useState/useEffect 1:42:04
Q56 1:42:39 What are React Hooks? What are the Top React
Hooks?
Q57 1:44:32 What are State, Stateless, Stateful and State
Management terms?
Q58 1:47:39 What is the role of useState() hook and how
it works?
Q59 1:52:08 What is the role of useEffect(). How it works
& what is its use?
Q60 1:56:13 What is Dependency Array in useEffect() hook?
Q61 1:58:25 What is the meaning of the empty array[] in
the useEffect()?
React- 8 Hooks -useContext/useReducer 1:59:12
Q62 1:59:53 What is the role of useContaxt() hook?
Q63 2:02:40 What is createContext() method? what are
Provider & Consumer Properties?
Q64 2:03:59 When to use useContext hook instead of props
in real application?
No Answer
Q65 what are the similarities between useState() &
useReducer() hook?
Q66 what is useReducer() hook? When to use useState() &
when useReducer()?
Q67 What are the differences between useState() &
useReducer() hook?
Q68 What are dispatch & reducer function in useReducer
hook?
Q69 What is the purpose of passing initial state as an
object in useReducer?
React 9 & 10 topics missing
React- 11 Component LifeCycle Method-1 2:05:24
Q70 2:06:12 What are component life cycle phases?
Q71 2:08:03 What are component life cycle methods?
Q73 2:09:55 What are constructors in class components ?
when to use them?
Q74 2:12:13 What is the role of super keyword in
constructor?
Q75 2:13:31 what is the role of render() method in
component life cycle?
Q76 2:15:30 How the state can be maintained in a class
component?
Q77 2:17:27 What is the role of componentDidMount()
method in component life cycle?
React 12 topics missing
React- 13 Controlled & Uncontrolled Components 2:20:39
Q78 2:20:53 What are controlled components in React?
Q79 2:23:17 What are the differences btw Controlled &
Uncontrolled components?
Q80 2:25:18 What are characteristics of controlled
components?
Q81 2:26:41 What are the advantages of using controlled
components in React forms?
Q82 2:28:41 How to handle forms in React?
Q83 2:28:55 How can you handle multiple input fields in a
controlled form?
Q84 2:29:11 How do you handle form validation in a
controlled component?
Q85 2:29:43 In what scenarios might using uncontrolled
components be advantageous?
React- 14 Code Splitting 2:30:13
Q86 2:30:50 What is code splitting in React?
Q87 2:32:45 How to implement code splitting in React?
Q88 2:35:58 What is the role of Lazy & Suspense methods
in React?
Q89 2:38:07 What are the Pros & Cons of code splitting?
Q90 2:41:39 What is the role of the import function in
code splitting?
Q91 2:42:06 What is the purpose of the fallback prop in
suspense?
Q92 2:42:32 Can you dynamically load css files using code
splitting in React?
Q93 2:42:55 How do you inspect & analyze the generated
chunks in React application?
React- 15 Others
Q94 2:43:58 What is a higher-order component in React?
Q95 2:47:03 What are the 5 Ways to Style React components
? Explain inline styles?
Q96 2:48:18 What are the difference between React & React
Native?
Q97 2:49:38 What is GraphQL?
Q98 2:50:45 What are the Top 3 ways to achieve state
management? when to use what in React?
Q99 2:53:34 How can you implement authentication in a
React application?
Q100 2:56:23 What is the use of React Profiler?
Q101 2:57:49 What is the difference between Fetch & Axios
for API calls in React?
Q102 3:00:34 What are the popular Testing Libraries for
React?
Q103 3:00:58 How can you Optimize Performance in React
application?
Q104 3:03:13 Explain Reactive Programming with example?
Q105 3:05:10 In how many ways can we implement Reactive
Programming in React?
Q106 3:06:20 How to pass data from child component to
parent component in React?

[Sasta_codeR]

TIMESTAMPS
2:42 react basics 1
26:45 react basics 2
48:24 react file and folders.
1:02:42 JSX
1:20:01 components- Functional/Class
1:34:11 Routing .
1:42:33 Hooks 1 .
1:59:28 Hooks 2.
2:05:49 life cycle methods-1
2:20:32 controlled & Uncontrolled Components .
2:30:15 code splitting
2:43:18 react -others

[zhewang]

I am a older mom with 2 kids, changing my career to a full stack developer. It is really hard for me to squeeze time learning all the technologies and compete with those young talents, but I am trying. Thank you so much for your videos, very self-explanatory! I just purchased your Udemy class for support! I will definitely let you know if I finally land a job~

[mrrickr]

I have selected as a software engineer by preparing with you videos 1.5 years ago.
Thanks.

[karthikkeyan]

Thankyou Happy, I crack the interview in my first try & waiting for the offer letter. This video is very useful for revision. Thankyou so much..

[neemasingh]

Attempted 12 interviews in 2 months, for Senior frontend dev, now I am here lets see how my other interviews go

[madhummh]

Hi sir from watching your videos and following your advice today I got my new job thank you very much sir In the interview almost all questions are asked that you taught only

[jaiswalsourabh]

Great React interview questions! 👍 Hoping for a follow-up with 100 Node.js questions. Your content is invaluable for developers! 🚀

[AshokKumar-pwue]

❤ from TamilNadu..
I got an offer from HCL for Fullstack role (DotNet + ReactJs)
Your videos are very very very helpful to clear the interviews.
Thank you so so so much for you.... 🙏🙏🙏🙏🙏☺☺☺

Keep posting, keep supporting...

[hurqkkn]

Q1. What is React? What is the Role of React in software development? Q2. What are the Key Features of React?
Q3. What is DOM? What is the difference between HTML and DOM? Q4. What is Virtual DOM? Difference between DOM and Virtual DOM? Q5. What are React Components? What are the main elements of it? Q6. What is SPA(Single Page Application)?
Q7. What are the 5 Advantages of React?
Q8. What are the Disadvantages of React?
Q9. What is the role of JSX in React? (3 points)
Q10. What is the difference between Declarative & Imperative syntax?


Q1. What is Arrow Function Expression in JSX? V. IMP.
Q2. How to Setup React first project?
Q3. What are the Main Files in a React project?
Q4. How React App Load and display the components in browser? V. IMP.
Q5. What is the difference between React and Angular?
Q6. What are other 5 JS frameworks other than React?
Q7. Whether React is a Framework or a Library? What is the difference?
Q8. How React provides Reusability and Composition?
Q9. What are State, Stateless, Stateful and State Management terms? Q10. What are Props n JSX? V. IMP.


Q1. What is NPM? What is the role of node_modules folder? V. IMP.
Q2. What is the role of public folder in React?
Q3. What is the role of src folder in React?
Q4. What is the role of index.html page in React?
V. IMP.
Q5. What is the role of index.js file and ReactDOM in React? V. IMP. Q6. What is the role of App.js file in React?
V. IMP.
Q7. What is the role of function and return inside App.js?
Q8. Can we have a function without a return inside App.js?
Q9. What is the role of export default inside App.js?
Q10. Does the file name and the component name must be same in React




Q1. What is the role of JSX in React? (3 points)
Q2. What are the 5 Advantages of JSX?
Q3. What is Babel?
Q4. What is the role of Fragment in JSX?
Q5. What is Spread Operator in JSX?
Q6. What are the types of Conditional Rendering in JSX? V. IMP.
Q7. How do you iterate over a list in JSX? What is map() method?
Q8. Can a browser read a JSX File?
Q9. What is Transpiler? What is the difference between Compiler & Transpile
Q10. Is it possible to use JSX without React?


Q1. What are React Components? What are the main elements of it?
V. IMP.
Q2. What are the Types of React components? What are Functional Components? V. IMP. Q3. How do you pass data between functional components in React?
Q4. What is Prop Drilling in React?
V. IMP.
Q5. Why to Avoid Prop Drilling? In how many ways can avoid Prop Drilling?
V. IMP.
V. IMP.
Q6. What are Class Components In React?
Q7. How to pass data between class components in React?
Q8. What is the role of this keyword in class components?
Q9. What are the 5 differences btw Functional components & Class components? V. IMP.


Q1. What is Routing and Router in React?
Q2. How to Implement Routing in React?
Q3. What are the roles of <Routes> & <Route> component in React Routing?
Q4. What are Route Parameters in React Routing?
Q5. What is the role of Switch Component in React Routing?
Q6. What is the role of exact prop in React Routing?



Q1. What are React Hooks? What are the Top React Hooks?
Q2. What are State, Stateless, Stateful and State Management terms? Q3. What is the role of useState() hook and how it works?
Q4. What is the role of use Effect(). How it works and what is its use?
Q5. What is Dependency Array in useEffect() hook?
Q6. What is the meaning of the empty array [] in the useEffect()?




Q1. What is the role of useContext() hook?
Q2. What is createContext() method? What are Provider & Consumer properties? Q3. When to use useContext() hook instead of props in real applications?
Q4. What are the similarities between useState() and useReducer() hook?
V. IMP.
Q5. What is useReducer() hook? When to use useState() and when useReducer()? V. IMP.
Q6. What are the differences between useState() and useReducer() Hook?
Q7. What are dispatch & reducer function in useReducer Hook?
Q8. What is the purpose of passing initial state as an object in UseReducer?



Q1. What are Component life cycle phases?
Q2. What are Component life cycle methods?
Q3. What are Constructors in class components? When to use them?
Q4. What is the role of super keyword in constructor?
Q5. What is the role of render() method in component life cycle?
Q6. How the State can be maintained in a class component?
Q7. What is the role of componentDidMount() method in component life cycle?




Q1. What are Controlled Components in React?
V. IMP.
Q2. What are the Differences btw Controlled & Uncontrolled Components? V. IMP. Q3. What are characteristics of controlled components?
Q4. What are the advantages of using controlled components in React forms?
Q5. How to handle forms in React?
Q6. How can you handle multiple input fields in a controlled form?
Q7. How do you handle form validation in a controlled component?
Q8. In what scenarios might using uncontrolled components be advantageous?



Q1. What is Code Splitting in React?
Q2. How to Implement Code Splitting in React?
Q3. What is the role of Lazy and Suspense methods in React? V. IMP.
Q4. What are the Pros and Cons of Code Splitting?
Q5. What is the role of the import() function in code splitting?
Q6. What is the purpose of the fallback prop in Suspense?
Q7. Can you dynamically load CSS files using code splitting in React?
Q8. How do you inspect and analyze the generated chunks in a React application?

[roshankarwalkar]

Thanks for this video, you have really covered all the common questions that every interviewer can ask for React and you are explainations are easy to understand.can you cover questions like
1.Diff in useMemo and useCallback
2.Does useCallback is needed in Ract 18
3.What are the new features are available in recent React version.
4.How to validate props in React.

[ishwar]

In last 6 month I have given 8 interviews in MNC and PBC all failed still not loosing hopes. Thanks for this video I appreciate your hard work!

[shreyasgowda]

Hi Happy, first i would like to thanks for efforts in making vedios which are helping thousands of people. I had 4 years as a .Net developer but when I started giving interviews i felt like am zero. But then i started watching your videos and now i have 4 offers and one in pipeline, whatever questions i used to get in interviews 98% of them were on ur channel. It helped me lot in my career and i have recommended it all my colleagues. Thanks a lot Happy… just like ur name says u made so many peoples life Happy 😊 all the best for ur channel and you ❤

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[rajeshRamakrishnan-phyi]

I have selected as a software engineer by preparing with you videos 8 months back

[kandycan]

I'm a full stack dotnet developer. The way you explained all the concepts answered more than just the questions i had in my mind initially. Great work 😄👍

[rajatchaurasia]

Thanks for sharing today is my Full stack of luck for me 🤞❤

[vinayaka]

Thank you sir most important topics coverd and all topics iam understand good explaination sir once again Tq you

[purneshvishnole]

we want same video of node.js of 200+ interview questions

[millenialKudi]

This is the best crash course for a react developer interview. I would recommend your course to all there.