60 MERN Stack Objective Type Quiz & MCQs with Answers for Interview Preparation | Gyansetu

Practice these MCQs to sharpen your MERN Stack development skills and prepare confidently for job interviews or certification exams.
Whether you’re aiming to crack full-stack developer roles or mastering MongoDB, Express.js, React, and Node.js for your next big project — you’re in the right place.

Get access to 60+ MERN Stack MCQs covering everything from REST APIs, React components, state management, backend logic, database queries, and deployment strategies — all with detailed answers to reinforce your understanding. No guesswork. Just solid prep.

🔵 1–15: MongoDB

1. Which command inserts a document into a collection named users?

A. db.users.add({name: “Amit”}) 
B. db.users.push({name: “Amit”}) 
C. db.users.insertOne({name: “Amit”}) 
D. db.insert.users({name: “Amit”})
✅ Answer: C
🧠 insertOne() adds a single document to the collection.

2. Which of these is used to find documents where age is greater than 25?

A. db.users.find({age: {$gt: 25}}) 
B. db.users.find({age: > 25}) 
C. db.users.where(age > 25) 
D. db.users.get({age: 25})
✅ Answer: A
🧠 $gt is MongoDB’s greater-than operator.

3. MongoDB stores data in:
   A. Rows
   B. Arrays
   C. BSON Documents
   D. Tables
   ✅ Answer: C
   🧠 MongoDB stores documents in BSON (Binary JSON).
4. What does the drop() method do?
   A. Deletes a field
   B. Removes a document
   C. Deletes a collection
   D. Deletes the database
   ✅ Answer: C
   🧠 drop() removes the entire collection.
5. Which operator matches any of the values specified in an array?
   A. $in
   B. $or
   C. $set
   D. $match
   ✅ Answer: A
   🧠 $in checks if a field’s value matches any value in a given array.
6. Which command shows all databases?
   A. show dbs
   B. show databases
   C. list dbs
   D. db.list()
   ✅ Answer: A
7. Which method removes a single document?
   A. delete()
   B. remove()
   C. deleteOne()
   D. drop()
   ✅ Answer: C
8. How do you update the name field to ‘John’?

db.users.updateOne({id: 1}, {$set: {name: "John"}})

A. Correct
B. Incorrect
✅ Answer: A

9. Which method returns a cursor in MongoDB?
   A. find()
   B. insertOne()
   C. drop()
   D. deleteMany()
   ✅ Answer: A
10. Which command removes all documents?
    A. deleteAll()
    B. removeAll()
    C. deleteMany({})
    D. clear()
    ✅ Answer: C
11. Which index type ensures field uniqueness?
    A. Default
    B. Compound
    C. Unique
    D. Text
    ✅ Answer: C
12. MongoDB is a:
    A. Relational DB
    B. Document-oriented DB
    C. Graph DB
    D. Column DB
    ✅ Answer: B
13. Which is true about ObjectId?
    A. String
    B. Timestamp + machine ID + counter
    C. Random number
    D. UUID
    ✅ Answer: B
14. Which method sorts query results?
    A. sort()
    B. orderBy()
    C. arrange()
    D. sequence()
    ✅ Answer: A
15. Which method limits the number of documents returned?
    A. slice()
    B. trim()
    C. limit()
    D. max()
    ✅ Answer: C

🟠 16–30: Express.js

16. What is Express.js?
    A. Frontend library
    B. MongoDB tool
    C. Web application framework
    D. Operating system
    ✅ Answer: C
17. Which method defines a GET route?

A. app.get(‘/path’, callback) 
B. app.route(‘/path’) 
C. app.GET(‘/path’, callback) 
D. route.get(callback)
✅ Answer: A

18. What is req.params used for?
    A. Query parameters
    B. Route parameters
    C. Headers
    D. Cookies
    ✅ Answer: B
19. How to send JSON response?

A. res.sendText(data) 
B. res.sendJSON(data) 
C. res.json(data) 
D. res.send(data, ‘application/json’)
✅ Answer: C

20. What is middleware?
    A. Component
    B. DB connection
    C. Function that runs before route
    D. Template
    ✅ Answer: C
21. Which port is used by default in Express apps?
    A. 5000
    B. 80
    C. 3000
    D. 27017
    ✅ Answer: C
22. How to import Express?

const express = require('express')

A. Correct
✅ Answer: A

23. How to handle errors in middleware?
    A. next()
    B. catch()
    C. next(err)
    D. res.end()
    ✅ Answer: C
24. Which is true about express.static()?
    A. Sends HTML
    B. Serves static files
    C. Parses cookies
    D. Creates API routes
    ✅ Answer: B
25. What does res.status(404).send() do?
    A. Sends error page
    B. Sends success
    C. Sends redirect
    D. Logs the request
    ✅ Answer: A
    
26. What does body-parser middleware do?
    A. Parses request body
    ✅ Answer: A
27. Which route handles POST request?

app.post('/submit', callback)

✅ Answer: A

28. What is req.query used for?
    A. POST data
    B. Route params
    C. Query string
    D. Headers
    ✅ Answer: C
29. What does next() do in middleware?
    A. Ends request
    B. Moves to next middleware
    ✅ Answer: B
30. Which method handles 404 errors?
    A. app.use() at the end
    ✅ Answer: A

🔵 31–45: React.js

31. React is a:
    A. MVC framework
    B. Library for UI
    ✅ Answer: B
32. How do you create a component?

function Hello() { return <h1>Hello</h1> }

✅ Answer: A

33. Which hook is used for state?
    A. useEffect()
    B. useRef()
    C. useState()
    ✅ Answer: C
34. JSX stands for:
    A. JavaScript XML
    ✅ Answer: A
35. What is the purpose of key in lists?
    A. Track changes
    ✅ Answer: A
36. ReactDOM renders to:
    A. Backend
    B. Virtual DOM
    C. Real DOM
    ✅ Answer: C
37. Which method is used to handle side effects?
    A. useEffect()
    ✅ Answer: A
38. Which is NOT a React hook?
    A. useData()
    ✅ Answer: A
39. State updates in React are:
    A. Synchronous
    B. Asynchronous
    ✅ Answer: B
40. Which of these is correct conditional rendering?

{isLoggedIn ? <Dashboard /> : <Login />}

const fs = require('fs')