MERN Stack Interview Questions & Preparation

MERN Stack developers are in high demand in businesses across sectors. They help companies build robust, dynamic, and user-friendly websites using technologies like MongoDB, Express.js, React, and Node.js.

Companies must hire skillful developers to make the most of the MERN technology to build websites that provide a superior user experience. And the best way to test the candidates' skills is to prepare the right MERN stack interview questions and answers.

In this blog, we've compiled top MERN stack developer interview questions to help you prepare and enable HRs to find the perfect candidate. The questions are distinguished for freshers and experienced developers.

Top 10 MERN Stack Developer Interview Questions

1. Can you explain the MERN stack and its components?
2. How do you handle backend routing in a MERN application?
3. How do you manage state in a MERN application, and what tools do you use for this?
4. Can you describe the process of connecting a React front-end with a Node.js backend?
5. How do you handle user authentication and authorization in a MERN application?
6. Can you give an example of how you would optimize the performance of a MERN application?
7. How do you implement real-time communication in a MERN application, such as WebSockets?
8. How would you deploy a MERN application to a production environment?
9. How do you test the components and functions of a MERN application?
10. Have you ever encountered a problem with the MERN stack, and if so, how did you resolve it?

MERN Stack Developer Interview Questions for Experienced Developers

Here is a list of MERN stack interview questions to thoroughly test candidates in a senior position:

1. What is a stub in Node.js?
2. Explain the concept of a thread pool. Which library handles it in Node.js?
3. What are smart components and dumb components?
4. What are the key features of NodeJS? What are its challenges?
5. What is occasion circle in NodeJS?
6. What do you understand by dependency injection? Why is it useful?
7. State the IDEs that are used in the development of Node.js.
8. What is REPL under Node.js? How does it work?
9. What is the difference between linear search and binary search?
10. What is the difference between Node.js, AJAX, and jQuery?
11. What do you understand by containerization?
12. What is a test pyramid? How do you actualize the test pyramid when examining HTTP APIs?
13. What is the purpose of indexing in MongoDB?
14. Explain the difference between classes and interfaces in TypeScript.
15. What are decorators in typescript? How to use them?
16. What do you understand by cross-site scripting?
17. What is AOT and JIT compiler in Angular?
18. What is the purpose of an event emitter under NodeJS?
19. What is NPM in NodeJS? What is its functionality?
20. What are Higher-Order Components (HOC) in React?
21. What is Callback Hell, and what is the leading cause of it?
22. How to avoid Callback Hell in Node.js?
23. How does Node.js handle child threads?
24. What is concurrency in Node.js? How does it work?
25. What is the difference between returning a callback and just calling a callback?
26. What is sharding in MongoDB? How to use it?
27. What is the difference between partition and sharding in MongoDB?
28. When should you consider embedding documents in MongoDB?
29. Can you have foreign keys in MongoDB? What is the alternative to a foreign key in MongoDB?
30. Explain the advantages of BSON over JSON in MongoDB.
31. How to use and manage MongoDB transactions?
32. What is an Aggregation Pipeline in MongoDB?
33. Why do you need Keys in React List? What are its benefits?
34. What are streams in Node.js? What are its types?
35. What are Node.js buffers?
36. What is blocking code in Node.js?
37. What is the purpose of super (props)?
38. What is the V8 Javascript engine? How does Node.js use it to run your code?
39. Can you rewrite promised-based applications to Async/Await in Node.js?
40. Can you list two arguments the async queue takes as input in Node.js?
41. How would you use validation on props in React?
42. Is Node.js single-threaded or multi-threaded? Please explain.
43. How to use classes in Node.js? Why should you use it?
44. What is the role of Libuv in Node?
45. Can you replace one field with another in MongoDB? If so, how?
46. What is the CAP theorem? Where does MongoDB stand in the CAP theorem?
47. Describe the non-blocking operations under Node.js.
48. What command is required to export external libraries to Node.js?
49. What is the purpose of the module exports in Node.js?
50. How can you achieve transaction lock in MongoDB?
51. What is JSX, and how does it work?
52. What is routing? How does routing work in Express.js?

MERN Stack Developer Interview Questions for Freshers

Here is the list of top MERN stack interview questions for freshers:

1. What is the purpose of MongoDB?
2. List some of the features of MongoDB.
3. What is the importance of the covered query in MongoDB?
4. What is the Mongo Shell?
5. How do you delete a document in MongoDB?
6. What is the default scope of the Node.js application?
7. Name of the functions of Node.js.
8. Which module is used for serving static resources in Node.js?
9. What is Express.js? Why should you use Express.js?
10. What is data modeling?
11. What is a grid system in web design? What are the most used grid systems?
12. What are the various functions performed by REPL?
13. Can you point out some of the benefits of AOT (ahead of time)?
14. How does React work?
15. Describe the advantages and limitations of React JS.
16. What are React hooks?
17. What are the advantages of using React Hooks?
18. Do Hooks replace HOCs and render props?
19. What are props in React?
20. What is reconciliation in ReactJS?
21. How is React different from Angular JS?
22. What is prop drilling in react.js? How to avoid it?
23. Discuss the significance of replication in MongoDB.
24. What do you understand by asynchronous API?
25. What are the differences between a Class component and a Functional component?
26. What is the difference between shadow DOM vs. virtual DOM?
27. What is an event loop in Node JS?
28. When should you use MongoDB vs. Redis?
29. How do you find documents with an array that contains a specific value?
30. What do you understand from occasion-driven programming?
31. Why should express app and server files be kept separately?
32. What are Pure components in React?
33. How do you query MongoDB with 'like'?
34. What is the difference between useRef and createRef in React.js?
35. Can you name some instances where you should not use Node.js?
36. Can you give an introduction to Mongoose for MongoDB?
37. What is Variable Scope in Javascript? Can you explain with an example?
38. What is the difference between linear search and binary search?

Before getting to the above MERN stack interview questions and answers, hiring managers should screen the candidates on skills relevant to MERN. For job seekers, preparing for these questions will give you a significant advantage in your next technical interview.