JavaScript Quiz Test Online (30 random Questions) 2025

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 the default state of a JavaScript promise?

A) Rejected

B) Resolved

C) Fulfilled

D) Pending

2 / 30

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

A) Resolves with all promises' results

B) Pauses until all promises are complete

C) Rejects all promises if one fails

D) Resolves with the fastest promise

3 / 30

3. Which method in JavaScript is used to create an AJAX request?

A) getRequest()

B) requestAPI()

C) fetch()

D) XMLHttpRequest()

4 / 30

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

A) parse()

B) parseInteger()

C) getInt()

D) parseInt()

5 / 30

5. What is the correct syntax to display an alert box in JavaScript?

A) msg("Hello");

B) alertBox("Hello");

C) display("Hello");

D) alert("Hello");

6 / 30

6. Which response type is used to receive data as JSON?

A) xml

B) json

C) text

D) blob

7 / 30

7. What is a secure way to handle sensitive API keys in JavaScript?

A) Store them in local storage.

B) Embed them in the HTML file.

C) Store them in plain text files.

D) Store them in the backend server.

8 / 30

8. What does the spread operator (...) do?

A) Splits arrays into individual elements

B) Expands iterable elements into individual values

C) Declares a rest parameter

D) Merges arrays into objects

9 / 30

9. What does the rest parameter (...) do?

A) Creates an object

B) Expands arrays into individual elements

C) Declares optional arguments

D) Condenses multiple arguments into an array

10 / 30

10. What does querySelector() do?

A) Selects the first matching element.

B) Selects all elements of a given type.

C) Selects elements by ID only.

D) Selects elements by class only.

11 / 30

11. What should you do before deploying a JavaScript application?

A) Minify and compress files.

B) Scan for vulnerabilities using automated tools.

C) Perform thorough testing.

D) All of the above.

12 / 30

12. Which of these is NOT a promise-based API?

A) Promise.any()

B) Promise.all()

C) fetch()

D) setTimeout()

13 / 30

13. How do you check if a property exists in an object?

A) property in obj

B) Both A and C

C) obj.property

D) obj.hasOwnProperty(property)

14 / 30

14. How can you determine the type of device being used?

A) Using the window.deviceType property.

B) Using the navigator.userAgent property.

C) Using the device.check() method.

D) Using the screen.type property.

15 / 30

15. Why is it important to set an expiration time for JWTs (JSON Web Tokens)?

A) To improve token generation speed.

B) To reduce server load.

C) To prevent unauthorized access after a specific time.

D) To simplify authentication.

16 / 30

16. What is event bubbling in JavaScript?

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

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

C) Events triggering only on the target element.

D) Events that do not propagate.

17 / 30

17. How do you cancel an interval set with setInterval()?

A) cancelInterval()

B) clearInterval()

C) stopInterval()

D) clearTimeout()

18 / 30

18. Which of the following is a common cause of memory leaks in JavaScript?

A) Using arrow functions.

B) Unreferenced closures.

C) Using const instead of var.

D) Event listeners not being removed.

19 / 30

19. What type of attack is prevented by using the X-Frame-Options header?

A) phishing

B) injection

C) clickjacking

D) sniffing

20 / 30

20. What does encapsulation mean in JavaScript?

A) Creating a copy of an object

B) Removing methods from an object

C) Combining multiple objects into one

D) Hiding data and exposing only the necessary parts of an object

21 / 30

21. Which function repeatedly executes code after a set interval?

A) setTimeout()

B) setRepeater()

C) executeLater()

D) setInterval()

22 / 30

22. Why is it important to use parameterized queries in JavaScript?

A) To simplify database queries.

B) To prevent SQL Injection attacks.

C) To improve code readability.

D) To reduce code execution time.

23 / 30

23. What does the window.scrollTo() method do?

A) Highlights the content on the page.

B) Saves the current scroll position.

C) Scrolls the document to a specific position.

D) Adjusts the browser zoom level.

24 / 30

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

A) A type of browser exploit.

B) A vulnerability in JavaScript frameworks.

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

D) An attack that steals cookies.

25 / 30

25. What does the map() method do in functional programming?

A) Filters elements based on a condition

B) Sorts the array

C) Transforms each array element and returns a new array

D) Mutates the original array

26 / 30

26. Which HTTP response code indicates a successful request?

A) 404

B) 301

C) 500

D) 200

27 / 30

27. What is the result of console.log(typeof NaN);?

A) "number"

B) "NaN"

C) "object"

D) "undefined"

28 / 30

28. What does NaN mean in JavaScript?

A) None of the above

B) Not a Number

C) Not a Null

D) Not a Name

29 / 30

29. What happens if you call stopPropagation() inside a capturing phase listener?

A) The event is ignored entirely.

B) The event propagation stops completely.

C) Only the target element receives the event.

D) The event continues in the bubbling phase.

30 / 30

30. What is the primary use of strict mode in JavaScript?

A) To optimize performance.

B) To prevent API misuse.

C) To enhance security by catching common coding errors.

D) To enforce HTTPS.

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