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. Which method is used to select an element by its ID in JavaScript?

A) querySelector

B) getElementsByTag

C) getElementByClass

D) getElementById

2 / 30

2. How do you stop event propagation in JavaScript?

A) event.clear()

B) event.stopPropagation()

C) event.preventPropagation()

D) event.preventDefault()

3 / 30

3. What is the output of console.log(1 + "2" + 3);?

A) 33

B) "6"

C) 6

D) "123"

4 / 30

4. What is the default content type for POST requests in AJAX?

A) multipart/form-data

B) text/plain

C) application/x-www-form-urlencoded

D) application/json

5 / 30

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

A) element.focused

B) document.hasFocus()

C) element.isFocused()

D) document.activeElement === element

6 / 30

6. What does await do in an async function?

A) Pauses the execution until the promise resolves

B) Creates a promise

C) Rejects a promise

D) Resolves a promise

7 / 30

7. Which method sends the AJAX request?

A) execute()

B) process()

C) send()

D) trigger()

8 / 30

8. What is the purpose of the timeout property in XMLHttpRequest?

A) To delay the request

B) To log the request duration

C) To specify the time before the request is automatically aborted

D) To control the server's response time

9 / 30

9. What is a potential risk of using inline JavaScript?

A) Difficulty in debugging.

B) Increased file size.

C) Reduced performance.

D) Exposure to XSS attacks.

10 / 30

10. Which readyState value indicates that the request is complete?

A) 4

B) 2

C) 1

D) 3

11 / 30

11. What does Object.create() do?

A) Copies an object

B) Creates a deep clone of an object

C) Creates a new object with the specified prototype

D) Returns a stringified version of an object

12 / 30

12. What is the default value of an uninitialized variable in JavaScript?

A) 0

B) NaN

C) null

D) undefined

13 / 30

13. How do you call the parent class constructor in a subclass?

A) constructor();

B) super();

C) parent();

D) base();

14 / 30

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

A) cancelInterval()

B) clearTimeout()

C) stopInterval()

D) clearInterval()

15 / 30

15. Which company developed JavaScript?

A) Netscape

B) Microsoft

C) Google

D) Sun Microsystems

16 / 30

16. What is JavaScript primarily used for?

A) Adding interactivity to web pages

B) Designing static websites

C) Server-side programming

D) Writing system-level software

17 / 30

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

A) Cancels an ongoing request

B) Closes the connection

C) Resends the request

D) Logs errors in the request

18 / 30

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

A) To simplify authentication.

B) To improve token generation speed.

C) To prevent unauthorized access after a specific time.

D) To reduce server load.

19 / 30

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

A) Resolves with the fastest promise

B) Pauses until all promises are complete

C) Rejects all promises if one fails

D) Resolves with all promises' results

20 / 30

20. What is the main drawback of callbacks?

A) All of the above

B) Difficult error handling

C) Poor readability

D) Callback hell (nested callbacks)

21 / 30

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

A) fetch()

B) requestAPI()

C) getRequest()

D) XMLHttpRequest()

22 / 30

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

A) msg("Hello");

B) alertBox("Hello");

C) alert("Hello");

D) display("Hello");

23 / 30

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

A) document.newElement()

B) document.generateElement()

C) document.addElement()

D) document.createElement()

24 / 30

24. Which of the following helps identify rendering performance issues?

A) Heap snapshots

B) Console tab

C) Lighthouse

D) Call stack

25 / 30

25. What is Cross-Site Scripting (XSS)?

A) A method for secure data encryption.

B) A technique for caching web pages.

C) A technique to improve web application performance.

D) An attack where malicious scripts are injected into web pages.

26 / 30

26. How do you register an event that triggers once and then removes itself?

A) Use the once option in addEventListener().

B) Use the triggerOnce() method.

C) Use the oneTimeEvent() function.

D) Use addEventListener() followed by removeEventListener().

27 / 30

27. What does the isNaN() function do?

A) Converts a string to a number.

B) Checks if a value is NaN.

C) Checks if a value is a number.

D) None of the above.

28 / 30

28. What does the performance.now() method return?

A) The user's system time.

B) The time since the browser was opened.

C) The time since the page started loading.

D) The current time in milliseconds.

29 / 30

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

A) It reduces performance.

B) It can introduce security vulnerabilities like XSS.

C) It doesn't work with modern browsers.

D) It is outdated.

30 / 30

30. Which keyword is used to define a constant in JavaScript?

A) constant

B) let

C) var

D) const

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