JavaScript Quiz Test Online (30 random Questions) 2026

Improve your JavaScript skills with this online quiz featuring 30 multiple-choice questions. Whether you’re a beginner or an experienced developer, this quiz covers JavaScript fundamentals, functions, objects, DOM manipulation, ES6 features, and asynchronous programming.

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30 Minutes JavaScript Quiz Test Online

Test your JavaScript knowledge with this 30-minute quiz! Covering fundamental to advanced concepts, this quiz features 30 multiple-choice questions that will challenge your understanding of variables, functions, objects, asynchronous programming, and DOM manipulation. Perfect for interview preparation and skill enhancement.

1 / 30

1. What is destructuring in ES6?

A) Concatenating arrays

B) Breaking arrays or objects into smaller parts

C) Modifying array elements

D) Copying objects

2 / 30

2. What is the purpose of the abort() method in AJAX?

A) Logs errors in the request

B) Closes the connection

C) Cancels an ongoing request

D) Resends the request

3 / 30

3. How can you check if an element has a specific class?

A) element.isClass(className)

B) element.hasClass(className)

C) element.containsClass(className)

D) element.classList.contains(className)

4 / 30

4. What is Cross-Site Request Forgery (CSRF)?

A) A vulnerability in JavaScript frameworks.

B) An attack that steals cookies.

C) A type of browser exploit.

D) An attack where unauthorized commands are executed on behalf of an authenticated user.

5 / 30

5. What does the HttpOnly flag on cookies do?

A) Prevents cookies from being accessed by client-side scripts.

B) Ensures cookies can only be accessed by JavaScript.

C) Extends the lifespan of cookies.

D) Encrypts cookie data.

6 / 30

6. Why should eval() be avoided in JavaScript?

A) It reduces performance.

B) It doesn't work with modern browsers.

C) It can introduce security vulnerabilities like XSS.

D) It is outdated.

7 / 30

7. Which tool is used for regression testing in JavaScript?

A) Mocha

B) Cypress

C) Puppeteer

D) Webpack

8 / 30

8. Which of the following is a correct way to write JavaScript in an HTML document?

A) <script href="script.js"></script>

B) <script src="script.js"></script>

C) <javascript src="script.js"></javascript>

D) <script-link src="script.js"></script-link>

9 / 30

9. What is event bubbling in JavaScript?

A) Events triggering in reverse order from the target element to the root.

B) Events triggering only on the target element.

C) Events that do not propagate.

D) Events triggering from the target element up to its ancestors.

10 / 30

10. What does the Notification API do?

A) Tracks the user's activity.

B) Updates the webpage title.

C) Sends notifications to the user's email.

D) Displays browser notifications.

11 / 30

11. How can developers avoid exposing sensitive information in source maps?

A) Avoid debugging tools.

B) Store source maps in cookies.

C) Use unminified files.

D) Disable source maps in production.

12 / 30

12. Which JavaScript method can help prevent XSS by escaping HTML?

A) sanitize

B) escape

C) encode

D) clean

13 / 30

13. How can you dynamically create a new DOM element in JavaScript?

A) document.addElement()

B) document.generateElement()

C) document.newElement()

D) document.createElement()

14 / 30

14. How can you prevent clickjacking attacks?

A) Use HTTPS.

B) Use strong passwords.

C) Avoid using iframes.

D) Use the X-Frame-Options header.

15 / 30

15. What is the purpose of the Secure flag in cookies?

A) To allow cookies to be accessed over HTTP.

B) To encrypt cookie data.

C) To prevent cookies from expiring.

D) To restrict cookies to HTTPS connections only.

16 / 30

16. What type of data is commonly used in an AJAX response?

A) JSON

B) All of the above

C) XML

D) Plain text

17 / 30

17. Which of the following is not a JavaScript data type?

A) Boolean

B) Number

C) String

D) Float

18 / 30

18. How can you remove an existing child element in the DOM?

A) clearChild()

B) removeElement()

C) removeChild()

D) deleteChild()

19 / 30

19. What is the responseType property used for in XMLHttpRequest?

A) To define the status code of the response

B) To define the format of the response

C) To set the request headers

D) To define the method used in the request

20 / 30

20. What does querySelector() do?

A) Selects elements by class only.

B) Selects the first matching element.

C) Selects elements by ID only.

D) Selects all elements of a given type.

21 / 30

21. What is the recommended way to validate user input?

A) hash

B) parse

C) sanitize

D) validate

22 / 30

22. How do you check the browser's viewport width in JavaScript?

A) document.body.width

B) screen.width

C) window.innerWidth

D) viewport.size

23 / 30

23. How do you create a custom animation using the Web Animations API?

A) Use element.animate() method.

B) Use animation.create() method.

C) Use window.createAnimation() method.

D) Use CSS.animate() method.

24 / 30

24. How can you detect if an element has focus?

A) document.hasFocus()

B) element.isFocused()

C) document.activeElement === element

D) element.focused

25 / 30

25. How does Object.entries() work in ES6?

A) Converts an object into a string

B) Returns an array of key-value pairs from an object

C) Creates an object clone

D) Merges two objects

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26. Which function is used to parse a string to an integer in JavaScript?

A) parse()

B) parseInt()

C) getInt()

D) parseInteger()

27 / 30

27. What is JSONP in the context of AJAX?

A) A JSON parser for browsers

B) A method to fetch JSON data from other domains

C) A replacement for XMLHttpRequest

D) A modern AJAX API

28 / 30

28. What does Object.create() do?

A) Creates a new object with the specified prototype

B) Copies an object

C) Creates a deep clone of an object

D) Returns a stringified version of an object

29 / 30

29. What happens if a promise is neither resolved nor rejected?

A) It resolves by default.

B) It throws an error.

C) It remains in a pending state.

D) It is deleted automatically.

30 / 30

30. What is the purpose of Promise.race()?

A) Pauses until all promises are complete

B) Resolves with all promises' results

C) Resolves with the fastest promise

D) Rejects all promises if one fails

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