Which Express JS Interview questions to prepare for practice?

Express.js Questions to Prepare for Practice

Practicing Express.js questions helps in mastering the core concepts, APIs, and real-world problem-solving skills associated with building server-side applications. Below is a categorized list of questions for effective preparation.

1. Basics of Express.js

• What is Express.js, and why is it used in Node.js?

• How do you create a simple Express server that listens on port 3000?

  const express = require("express");
  const app = express();
  
  app.get("/", (req, res) => {
    res.send("Hello, World!");
  });
  
  app.listen(3000, () => {
    console.log("Server running on port 3000");
  });

• What are the main features of Express.js?

• How does Express.js differ from Node.js?

2. Routing in Express.js

• How do you define routes in Express.js?

• Write an example of route parameters in Express.js.

  app.get("/user/:id", (req, res) => {
    res.send(`User ID: ${req.params.id}`);
  });

• How can you define middleware for specific routes?

• What is the difference between app.use() and app.get()?

3. Middleware in Express.js

• What is middleware in Express.js, and how is it used?

• How do you create and use custom middleware?

  const logger = (req, res, next) => {
    console.log(`${req.method} ${req.url}`);
    next();
  };
  
  app.use(logger);

• What is the difference between application-level and router-level middleware?

• How can you handle errors using middleware?

4. Request and Response Handling

• How do you access query parameters in an Express route?

  app.get("/search", (req, res) => {
    res.send(`Search query: ${req.query.q}`);
  });

• How do you send JSON responses in Express.js?

• Write an example of handling file uploads in Express.js.

5. Express.js with Databases

• How do you connect Express.js with MongoDB?

  const mongoose = require("mongoose");
  
  mongoose.connect("mongodb://localhost:27017/mydb", { useNewUrlParser: true });
  
  app.get("/data", async (req, res) => {
    const data = await MyModel.find();
    res.json(data);
  });

• How do you perform CRUD operations in Express.js with a database?

• What are the best practices for structuring database logic in an Express application?

6. Authentication and Security

• How do you implement user authentication in an Express.js application?

• Write an example of using JWT for authentication.

  const jwt = require("jsonwebtoken");
  
  app.post("/login", (req, res) => {
    const token = jwt.sign({ userId: req.body.id }, "secretKey");
    res.json({ token });
  });

• What is CORS, and how do you enable it in an Express application?

  const cors = require("cors");
  app.use(cors());

• How do you secure sensitive data in an Express.js application?

7. Error Handling

• How do you handle errors in Express.js applications?
• Write an example of using an error-handling middleware.

  app.use((err, req, res, next) => {
    console.error(err.stack);
    res.status(500).send("Something went wrong!");
  });

8. Advanced Topics

• How do you set up an Express.js project using express-generator?
• How do you implement real-time features in Express.js with WebSockets?
• What is the role of req and res in Express.js, and how can you extend their functionality?

9. Real-World Scenarios

• Design an API endpoint to fetch paginated results.
• How would you handle file downloads in an Express.js application?
• Write an Express.js RESTful API for a basic CRUD application.

10. Testing in Express.js

• How do you test Express.js routes using tools like Mocha or Jest?
• Write a test case to verify the response of an API endpoint.

  const request = require("supertest");
  const app = require("./app");
  
  describe("GET /", () => {
    it("should return Hello, World!", async () => {
      const res = await request(app).get("/");
      expect(res.text).toBe("Hello, World!");
    });
  });

Recommended Resources

• Grokking the Coding Interview: Patterns for Coding Questions: Enhance problem-solving skills relevant for back-end interviews. Explore the course
• Grokking System Design Interview: Learn how to structure scalable Express.js applications. Check it out

By practicing these questions and working on small projects, you'll be well-prepared for Express.js interviews and capable of building robust back-end applications.