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 HTTP method is idempotent?

A) GET

B) DELETE

C) POST

D) PUT

2 / 30

2. How can you handle both the response and errors in the Fetch API?

A) Using then() and catch()

B) Using catch() only

C) Using finally()

D) Using then() only

3 / 30

3. Which statement correctly defines a function in JavaScript?

A) def myFunction() {}

B) function myFunction() {}

C) function: myFunction() {}

D) fun myFunction() {}

4 / 30

4. What is polymorphism in JavaScript?

A) Inheriting properties from multiple classes

B) Creating multiple instances of a class

C) Having multiple methods with the same name but different implementations

D) None of the above

5 / 30

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

A) property in obj

B) obj.property

C) obj.hasOwnProperty(property)

D) Both A and C

6 / 30

6. What does the history.pushState() method do?

A) Redirects to a new URL.

B) Clears the browser history.

C) Modifies the browser history without reloading the page.

D) Fetches the current page title.

7 / 30

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

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

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

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

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

8 / 30

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

A) executeLater()

B) setInterval()

C) setRepeater()

D) setTimeout()

9 / 30

9. What is asynchronous JavaScript?

A) Code executed line by line in order

B) Code executed in parallel without blocking

C) Code executed without using variables

D) Code executed only after page load

10 / 30

10. Which of the following methods correctly copies an array in JavaScript?

A) let newArr = oldArr.slice();

B) Both B and C

C) let newArr = oldArr;

D) let newArr = [...oldArr];

11 / 30

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

A) To define the format of the response

B) To define the status code of the response

C) To set the request headers

D) To define the method used in the request

12 / 30

12. Which of the following is a JavaScript framework/library?

A) Flask

B) Laravel

C) Django

D) React

13 / 30

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

A) Use element.animate() method.

B) Use window.createAnimation() method.

C) Use CSS.animate() method.

D) Use animation.create() method.

14 / 30

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

A) Unreferenced closures.

B) Using const instead of var.

C) Using arrow functions.

D) Event listeners not being removed.

15 / 30

15. What does the Notification API do?

A) Updates the webpage title.

B) Tracks the user's activity.

C) Displays browser notifications.

D) Sends notifications to the user's email.

16 / 30

16. 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().

17 / 30

17. What does const keyword do?

A) Both B and C

B) Declares a variable that cannot be reassigned

C) Declares a variable with block scope

D) Declares a constant variable with global scope

18 / 30

18. What does await do in an async function?

A) Pauses the execution until the promise resolves

B) Resolves a promise

C) Creates a promise

D) Rejects a promise

19 / 30

19. Which is NOT true about Promise.finally()?

A) It can be used for cleanup.

B) It runs only on a rejected promise.

C) It executes after the promise is settled.

D) It does not modify the resolved value.

20 / 30

20. Which modern API is a simpler alternative to XMLHttpRequest?

A) Event API

B) Fetch API

C) WebSockets

D) DOMParser

21 / 30

21. What is the purpose of the fetch() API?

A) To fetch local files.

B) To fetch cookies.

C) To make HTTP requests.

D) To fetch browser settings.

22 / 30

22. What does the navigator.geolocation.getCurrentPosition() method do?

A) Fetches the current time.

B) Retrieves the user's current location.

C) Updates the user's address.

D) Sets the user's location.

23 / 30

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

A) To prevent unauthorized access after a specific time.

B) To reduce server load.

C) To simplify authentication.

D) To improve token generation speed.

24 / 30

24. How can you write a multi-line comment in JavaScript?

A) // Comment

B) /* Comment // Comment */

C) /* Comment */

D)

25 / 30

25. Which method adds an event listener to an element?

A) attachListener()

B) addEventListener()

C) addListener()

D) registerEvent()

26 / 30

26. What does the crypto.randomUUID() method do?

A) Creates a random number.

B) Decrypts a string.

C) Generates a unique identifier.

D) Encrypts a string.

27 / 30

27. Which method is used to store data in the browser's local storage?

A) storeData()

B) localStorage.setItem()

C) browserData.set()

D) sessionStorage.setItem()

28 / 30

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

A) Merges arrays into objects

B) Expands iterable elements into individual values

C) Declares a rest parameter

D) Splits arrays into individual elements

29 / 30

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

A) deleteChild()

B) removeChild()

C) removeElement()

D) clearChild()

30 / 30

30. Which method is used to add an event listener to an element?

A) element.onEvent()

B) element.addEventListener()

C) element.bindEvent()

D) element.attachEvent()

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