Top 66 Mern Stack Interview Questions And Answers

1. How does React work?
2. What are React Hooks?
3. What are props in React?
4. What are the advantages of ReactJS?
5. How is React different from Angular JS?
6. What is Replication in MongoDB?
7. What are Higher-Order Components in React?
8. What are advantages of using React Hooks?
9. What are the limitations of React?
10. What are the differences between a class component and Functional component?
11. What are the key features of Node.js?
12. What do you mean by Asynchronous API?
13. What is Callback Hell and What is the main cause of it?
14. What is Reconciliation in ReactJS?
15. What is Sharding in MongoDB?
16. What is the difference between returning a callback and just calling a callback?
17. When should we embed one document within another in MongoDB?
18. Does MongoDB support Foreign Key Constraints?
19. Explain advantages of BSON over JSON in MangoDB?
20. Given the React code defined above, can you identify two problems?
21. How can you achieve Transaction in MongoDB?
22. What does Node.js handle Child Threads?
23. How does concurrency work in Node.js?
24. How to avoid Callback Hell in Node.js?
25. How do you handle backend routing in a MERN application?
26. How do you manage state in a MERN application, and what tools do you use for this?
27. Can you describe the process of connecting a React front-end with a Node.js backend?
28. How do you handle user authentication and authorization in a MERN application?
29. Can you give an example of how you would optimize the performance of a MERN application?
30. How do you implement real-time communication in a MERN application, such as WebSockets?
31. How would you deploy a MERN application to a production environment?
32. How do you test the components and functions of a MERN application?
33. Have you ever encountered a problem with the MERN stack, and if so, how did you resolve it?
34. Check out our tailor-made MERN Stack Developer Test, which can be customized to screen candidates before the interview.
35. MERN Stack Developer Interview Questions for Experienced Developers
36. Here is a list of MERN stack interview questions to thoroughly test candidates in a senior position:
37. What is a stub in Node.js?
38. Explain the concept of a thread pool. Which library handles it in Node.js?
39. What are smart components and dumb components?
40. What are the key features of NodeJS? What are its challenges?
41. What is occasion circle in NodeJS?
42. What do you understand by dependency injection? Why is it useful?
43. State the IDEs that are used in the development of Node.js.
44. What is REPL under Node.js? How does it work?
45. What is the difference between linear search and binary search?
46. What is the difference between Node.js, AJAX, and jQuery?
47. What do you understand by containerization?
48. What is a test pyramid? How do you actualize the test pyramid when examining HTTP APIs?
49. What is the purpose of indexing in MongoDB?
50. Explain the difference between classes and interfaces in TypeScript.
51. What are decorators in typescript? How to use them?
52. What do you understand by cross-site scripting?
53. What is AOT and JIT compiler in Angular?
54. What is the purpose of an event emitter under NodeJS?
55. What is NPM in NodeJS? What is its functionality?
56. What are Higher-Order Components (HOC) in React?
57. What is Callback Hell, and what is the leading cause of it?
58. How to avoid Callback Hell in Node.js?
59. How does Node.js handle child threads?
60. What is concurrency in Node.js? How does it work?
61. What is the difference between returning a callback and just calling a callback?
62. What is sharding in MongoDB? How to use it?
63. What is the difference between partition and sharding in MongoDB?
64. When should you consider embedding documents in MongoDB?
65. Can you have foreign keys in MongoDB? What is the alternative to a foreign key in MongoDB?
66. What is an event loop in Node JS?

Mern Stack Interview Questions And Answers

1. How does React work?
   Ans.React is a JavaScript library for building user interfaces. It uses a virtual DOM to efficiently update the actual DOM. React components represent different parts of a user interface and can be reused throughout an application. React maintains a virtual DOM in memory, compares it with the actual DOM, and updates only the parts that have changed, which makes the process more efficient.
2. What are React Hooks?
   Ans.React Hooks are functions that let you use state and other React features in functional components. They were introduced in React 16.8 to allow developers to use state and lifecycle features in functional components, which were previously exclusive to class components. Commonly used hooks include useState, useEffect, and useContext.
3. What are props in React?
   Ans. Props (short for properties) are a way to pass data from a parent component to a child component in React. They are read-only and help in communication between components. Props are passed down the component tree, allowing for the creation of dynamic and reusable components.
4. What are the advantages of ReactJS?

Ans.

• Virtual DOM: Improves performance by minimizing direct manipulation of the actual DOM.
• Component-Based: Encourages modular and reusable code through components.
• Declarative Syntax: Simplifies the process of understanding and writing UI code.
• One-Way Data Binding: Makes it easier to manage and track the flow of data.
• Community and Ecosystem: Large and active community, extensive libraries, and support.

5.How is React different from Angular JS?

Ans.

• Language: React uses JavaScript (or JSX), while Angular uses TypeScript.
• Architecture: React is just a library for the view layer, while Angular is a full-fledged MVC framework.
• Data Binding: React uses one-way data binding, and Angular uses two-way data binding.
• DOM Manipulation: React uses a virtual DOM, while Angular directly manipulates the real DOM.
• Learning Curve: React is generally considered easier to learn than Angular.

6.What is Replication in MongoDB?

Ans.
Replication in MongoDB is the process of synchronizing data across multiple servers to ensure high availability and fault tolerance. It involves maintaining multiple copies of the data on different servers, known as replica sets. In case one server goes down, another can take over, ensuring continuous availability.

7.What are Higher-Order Components in React?

Ans.
Higher-Order Components (HOCs) are functions that take a component and return a new component with enhanced features. HOCs are a way to reuse component logic, share code between components, and abstract complex behavior into a separate component.

8.What are advantages of using React Hooks?

Ans.

• Simplifies State and Lifecycle Management: useState and useEffect make it easier to manage component state and lifecycle in functional components.
• Encourages Reusability: Hooks allow the reuse of stateful logic across multiple components.
• Reduces Boilerplate Code: Hooks often result in less code compared to equivalent class components.
• Enhanced Readability: Hooks can make the code more readable and easier to understand.

9.What are the limitations of React?

Ans.

• Learning Curve: While React itself is relatively simple, the ecosystem and associated tools may have a learning curve.
• Overhead: React applications may have a larger initial bundle size compared to some other frameworks.
• JSX: Some developers may find JSX syntax unusual or challenging initially.
• SEO: React applications may require additional effort for search engine optimization.

10. What are the differences between a class component and a Functional component?

Ans.

• Syntax: Class components use the ES6 class syntax, while functional components are just JavaScript functions.
• State and Lifecycle: Class components can have local state and lifecycle methods, whereas functional components can use hooks for state and lifecycle functionality.
• Readability: Functional components are often considered more concise and easier to read.
• Performance: Functional components with hooks may have better performance due to the absence of some overhead associated with class components.

11. What are the key features of Node.js?

Ans.

• Asynchronous I/O: Non-blocking I/O operations for efficient handling of concurrent requests.
• Event-Driven: Uses an event-driven, asynchronous model.
• Single-Threaded: Utilizes a single-threaded event loop for handling multiple concurrent connections.
• Cross-Platform: Runs on multiple platforms like Windows, Linux, and macOS.
• NPM (Node Package Manager): A vast ecosystem of open-source libraries and modules.

12.What do you mean by Asynchronous API?

Ans.
An asynchronous API (Application Programming Interface) allows certain operations to be performed asynchronously. In the context of web development, this often involves making requests to servers or executing code without blocking the main thread. Asynchronous APIs use mechanisms like callbacks, promises, or async/await to handle asynchronous operations.

13.What is Callback Hell and What is the main cause of it?

Ans.
Callback Hell, also known as “Pyramid of Doom,” refers to the situation where multiple nested callbacks make the code difficult to read and maintain. It occurs when handling asynchronous operations using callbacks within callbacks within callbacks, creating a deep and indented structure. The main cause is the nature of JavaScript’s callback-based approach for handling asynchronous tasks, which can lead to deeply nested and hard-to-follow code.

14.What is Reconciliation in ReactJS?

Ans.
Reconciliation in React is the process of updating the DOM to match the virtual DOM when there are changes in a component’s state or props. React’s diffing algorithm (a part of the reconciliation process) efficiently determines the minimal number of changes needed to update the DOM. This helps in optimizing performance by avoiding unnecessary updates to the actual DOM, making the UI updates more efficient.