Top 100 MERN Stack Developer Interview Questions

MERN Stack developers are in high demand in businesses across sectors. They help companies build a robust, dynamic, and user-friendly websites using technologies like JavaScript, HTML5, CSS3, etc.

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 100 MERN stack developer interview questions to 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?

Check out our tailor-made MERN Stack Developer Test, which can be customized to screen candidates before the interview.

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. Here are a few iMocha skills tests to select the right candidates for the interview:

• Java Script Coding Test
• Full Stack. Net Developer Test
• Java Full Stack Developer Skill Test 
• MongoDB Test 
• Express.js Test 
• React.js Test 

Tips for interviewing MERN Stack Developers

Besides asking the right MERN stack developer interview questions, hiring managers should consider a few other things when hiring technical candidates. Here are a few tips for them:

1. Put the Applicant at Ease:
Before getting down to the hard MERN stack interview questions and answers, hiring managers should try to build a rapport with the candidate by asking a few personal questions.

Eye contact and a smile go a long way. It's best to review the resume beforehand to make a good start.

2. Ask Some Open-Ended Questions
The most interesting responses often come from open-ended questions such as:

• Why did you leave your last position?
• Where do you see yourself in five years?
• What accomplishments are you proud of?

Ask the same questions to all interviewees and compare their responses. If the application gives general answers, dig for more detail.

3. Let Candidates Do Most of the Talking
As a thumb rule, hiring managers should only talk thirty percent of the time. Listen carefully to the candidates answer MERN stack interview questions and take notes. It will help evaluate the answers and ask follow-up questions.

4. Conduct Live Coding Tests
Live coding tests are among the most popular ways to test candidates' abilities. Hiring managers can set a problem or task and watch how the candidate solves it through screen-sharing.

You can hire the best coders using iMocha's live coding interview feature.

5. Follow Up
Do not forget to inform the candidates whether they got the job as a professional courtesy. It helps give the interview process closure for the candidates.

Final Words

So these are the common MERN stack developer interview questions asked to evaluate the candidate's MERN stack skills. Keep in mind that the exact questions need to be asked based on the specific requirement of the job and the company.

Inefficient screening processes and technical evaluations deprive organizations of the most deserving candidates. This is where iMocha comes to the rescue.

iMocha is a skilled assessment platform for hiring talent fast and at scale. It enables organizations to make data-driven, skilled-based, and biased-free hiring.

Here's how companies can benefit from iMocha:

• Screen the best candidates for interviews.
• Choose assessments from a library of 2500+ skills.
• Evaluate technical skills through live coding/programming interviews.
• Measure technical competencies through intelligent talent analytics.
• Hire global talent through iMocha's remote hiring solution.
• Consistently engage candidates through a hoard of engagement features.

Ready to hire the best MERN stack developer for your business? Book a free demo with iMocha.

FAQs

What are the skills required for a MERN Stack developer?
The major skills required for a MERN stack developer are front-end technology (React.js), Node.js, Express.js, backend development, and database management.

Hiring managers should prepare MERN stack interview questions and answers that test these skills.

Which language is used in MERN?
MongoDB, Express.js, React, and Node.js are all JavaScript frameworks. Hence, MERN stack developers can build the entire web application in a single programming language, JavaScript.

Which language is learned first in the MERN stack?
Javascript is the first language learned in MERN Stack.