Whatever you studied, whatever your qualifications are, isn’t getting you anywhere without cracking an interview. Though the idea of presenting yourself in 30 minutes doesn’t uncover your full potential and gets you judged on whether you are worth hiring, it is still a skill to brief out about yourself and be confident enough to do so as well. Knowing and answering relevant questions is also important to show how much you have prepared yourself. What you know isn’t relevant unless it is expected of you in the role or asked of you in a specific interview. Preparing for these questions is a great way to showcase your knowledge and get hired. Here are the most common MERN stack interview questions for you to prepare for your next interview.
What is MERN Stack?
Understanding what is MERN Stack is must be the most substantial thing even before preparing for the interview. What is MERN Stack is also a common MERN stack interview question to be prepared for. MERN stack is a JavaScript solution for building strong and functioning web applications. MERN stack gets its name from frameworks, databases and others that use a single language, JavaScript. They include MongoDB, Express.js, React and Node.js, forming the name MERN. Let’s take a look at them in detail. Make sure to learn and understand in order to confidently answer MERN stack interview questions.
- What is MongoDB?
In simple terms, MongoDB is a NoSQL document database that stores data in documents like JSON. Its use case includes Dynamic Schema, horizontal scaling and real-time analysis. Key features are BSON storage, built-in replication and sharding.
- What is Express.js?
Express.js is a framework extensively used by Nord.js. It handles HTTP requests and middleware. The use cases of Express.js involve building RESTui APIs, routing and middleware pipelines. Its key features are its lightweigh,t extensibl,e and middleware modules
- What is React?
React is a component-based library tailored for front-end development to create interactive UI’s. Single-page application (SPA) and dynamic client-side rendering are one of its major use cases. It comes with key features such as Virtual DOM, reusable components, hooks for state and side effects.
- What is Node.js?
Node.js is a JavaScript run-time that is created on Chrome’s V8 engine, running server-side code. Common use cases of Node.js are non-blocking, event-driven servers for applications that run in real-time. Packaged eco-system via npm, event loop for high concurrency are its key features.
Hope these have polished your information on MERN stack. Expect these common questions on MERN stack interviews as well. Let’s take a look at the other common MERN stack interview questions.
Why Use MERN?
This question could be the most asked in a MERN stack interview. Why use MERN would let you answer what you know about it, its relevance and why MERN is a better alternative for many. You can learn and answer these in your own style, tone or variation.
- Having JavaScript across the whole stack and no context-switching between languages makes MERN a great choice.
- With thousands of npm packages and React libraries, MERN possesses a rich ecosystem.
- The MongoDB documents and Express/Node APIs come with a JSON and React client with horizontal scaling via Node Clusters and MongoDB sharding
- Another reason to use MERN is its strong community and resources, such as its support, tutorials and boilerplates.
Typical MERN Architecture
Another common MERN interview question is the typical MERN architecture, you may have to answer regarding the client, server, Database and its build and deployment in detail. You can learn and answer from the resource below.
- The client is React, which renders UI components and manages client-side routing with the React Router. It also communicates with the server via fetch/axios
- Express and Node make the server with it, defining RESTful endpoints and implementing business logic. The server also handles authentication, validation and error handling.
- MongoDB makes up the database of MERN and is responsible for storing user data, application state, product catalogues and much more. The database is managed via a MongoDB driver or ODM such as Mongoose.
- Build and deployment uses Webpack/vite build for React, PM2 or Docker for Node processes and CI/CD pipelines like GitHub Actions and Jenkins.
After you have understood these well take note of the short and simple MERN stack interview questions, with answers to help you out.
MERN Stack Interview Questions
1. Why choose MongoDB over a relational database?
You can answer like: Choosing MongoDB over a relational database offers schema flexibility, letting documents evolve without migrations. Having MongoDB can also enable Horizontal scaling, which is native sharding for large datasets. It also possesses JSON-like documents that align well with JS objects in Node and React.
2. What role does Express.js play?
The answer to this is simple, the role of Express.js assists in routing maps HTTP methods as well as URLs to handlers. It also serves as a middleware for pre- and post-processors for requests such as logging, auth and so on. Additionally, Express.js manages error handling, and centralises error response and logging.
3. How do you manage state in React?
The states in React are divided into Local state, global state and server state. For managing the Local state, use “useState” or “useReducer” for the component-level state. For the Global state, use Context API or external libraries (Redux, Zustand, MobX), and finally for Server state, Data fetching from libraries like React, Query and SWR would be ideal.
4. Describe the Node.js event loop
The Node.js event loop is a single-threaded loop handling asynchronous callbacks. It also has phases like timers, I/O callbacks, idle/prepare, poll check and close callbacks, enabling high concurrency by avoiding blocking calls.
5. What is middleware in Express?
A middleware in MERN is a function with a signature (req, res, next) that can modify req/res, end the request and send a response as well as call next() in order to pass or control to the next middleware.
6. Explain JWT authentication flow
These are amongst the most commonly asked questions in a MERN stack interview. You can answer by explaining JWT authentication and then the flow. Start answering by saying, this is a commonly used authentication mechanism in modern web applications. They work by securely transmitting information between a client and a server in the form of a compact JSON object. JWTs are often used for stateless authentication, where the server does not need to keep a record of the user’s session. The flow is as follows:
- The user logs in, and the server is verified
- Then the server issues a signed certificate containing the user’s claims
- Next in the flow, the client stores a token, such as a cookie or localStorage
- It’s followed by subsequent requests, including a token in authorization header
- The server then verifies the token signature, extracting the user info
7. How do you optimise React performance
That’s a great question! You may say this as it showcases your confidence and expertise in the MERN stack in a MERN stack interview. The simple answer to this question is;
Monetisation using React.memo, useMemo, useCallback and Code Splitting with import() and React. lazy. You can avoid unnecessary renders, such as Key prop, immaculate data and pure components
8. Can you describe how to model relationships in MongoDB?
There are three ways to model relationships in MongoDB: embedding, Referencing and using Mongoose’s “populate()” to join on queries. Embedding sub-documents for one-to-few relationships and referencing by storeobjectid references, such as one-to-many or many-to-many.
9. What is Mongoose and why use it?
Understanding this is essential in MERN. Mongoose is an Object Data Modelling (ODM) library for MongoDB and Node.js. It is useful for providing schema definitions and data validation. Mongoose also offers middleware hooks like before/after save as well as update. The prominent use of Mongoose, and if asked why to use it, must be answered by its ability to simplify queries and relationships.
10. How would you deploy a MERN app?
MERN stack interview questions can be hard at times, but knowing plenty wouldn’t help if you can’t answer them the right way. Being able to answer in a good flow is crucial as well. To answer this MERN Stack interview question, do it step by step:
- Back end: Dockerize Node app by pushing to AWS, ECS/EKS, Heroku or DigitalOcean
- Database: with a database like MongoDB Atlas or a managed Mongo service.
- Front end: build React bundle and serve via CDN or static hosting using tools like Netlify, Vercel
- Finally, to deploy a MERN app, use CI/CD to automate builds and tests using GitHub, Actions or Jenkins.
To conclude, preparing for the above-mentioned MERN interview questions would put you in an advantageous position. Though doing research is also significant, these are the most common questions, but you should realise there are more and predict what might be difficult. Additionally, be confident, have a great portfolio, and be prepared to work on some live projects to showcase your skills
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