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 JavaScript primarily used for?

A) Designing static websites

B) Adding interactivity to web pages

C) Server-side programming

D) Writing system-level software

2 / 30

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

A) Event API

B) Fetch API

C) WebSockets

D) DOMParser

3 / 30

3. Which storage type is most vulnerable to XSS attacks?

A) cache

B) sessionStorage

C) localStorage

D) cookies

4 / 30

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

A) fetch()

B) XMLHttpRequest()

C) requestAPI()

D) getRequest()

5 / 30

5. What is polymorphism in JavaScript?

A) Inheriting properties from multiple classes

B) None of the above

C) Creating multiple instances of a class

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

6 / 30

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

A) Retrieves the user's current location.

B) Updates the user's address.

C) Fetches the current time.

D) Sets the user's location.

7 / 30

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

A) Use the once option in addEventListener().

B) Use the oneTimeEvent() function.

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

D) Use the triggerOnce() method.

8 / 30

8. What is a secure way to store sensitive data in the browser?

A) Cookies without flags

B) Encrypted cookies with HttpOnly and Secure flags

C) Local storage

D) Plain JavaScript variables

9 / 30

9. Which keyword is used to define a class in JavaScript?

A) class

B) object

C) new

D) define

10 / 30

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

A) sniffing

B) phishing

C) clickjacking

D) injection

11 / 30

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

A) Encrypts a string.

B) Decrypts a string.

C) Generates a unique identifier.

D) Creates a random number.

12 / 30

12. Which HTTP response code indicates a successful request?

A) 301

B) 404

C) 500

D) 200

13 / 30

13. How do you add a new attribute to an element in JavaScript?

A) element.createAttribute(name, value)

B) element.setAttribute(name, value)

C) element.attribute(name, value)

D) element.addAttribute(name, value)

14 / 30

14. What is the purpose of minifying JavaScript files?

A) To improve code readability.

B) To detect syntax errors.

C) To reduce file size for faster loading.

D) To add comments to the code.

15 / 30

15. Which API is used to measure page load times?

A) Web Animations API

B) Performance API

C) Event Loop API

D) MediaStream API

16 / 30

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

A) Using catch() only

B) Using then() and catch()

C) Using finally()

D) Using then() only

17 / 30

17. What is the purpose of the focus event in JavaScript?

A) It triggers when a mouse hovers over an element.

B) It triggers when a user types inside an element.

C) It triggers when an element gains focus.

D) It triggers when an element loses focus.

18 / 30

18. What is the primary purpose of Content Security Policy (CSP)?

A) To prevent unauthorized file downloads.

B) To enforce HTTPS.

C) To restrict API usage in JavaScript.

D) To mitigate XSS attacks by controlling resources a browser can load.

19 / 30

19. What is the purpose of the window.requestAnimationFrame() method?

A) To stop animations.

B) To reload the page.

C) To optimize animations by syncing with the screen refresh rate.

D) To create animations.

20 / 30

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

A) To enforce HTTPS.

B) To prevent API misuse.

C) To enhance security by catching common coding errors.

D) To optimize performance.

21 / 30

21. What is lazy loading in performance optimization?

A) Delaying loading of resources until they are needed.

B) Preloading all images in the background.

C) Minimizing HTTP requests.

D) Loading all assets upfront.

22 / 30

22. What does the window.open() method do?

A) Navigates to a new URL in the same window.

B) Opens a new browser tab or window.

C) Reloads the current page.

D) Closes the current window.

23 / 30

23. How can you write a comment in JavaScript?

A) /$ This is a comment $/

B) # This is a comment

C) /* This is a comment */

D)

24 / 30

24. What is the difference between == and === in ES6?

A) == checks only value; === checks type and value

B) == checks type and value; === checks only value

C) No difference

D) Both perform type coercion

25 / 30

25. What does the credentials option in the Fetch API specify?

A) Cache policy

B) Request timeout

C) Include cookies in requests

D) Redirect behavior

26 / 30

26. Which method is used to add an element to the end of an array?

A) push()

B) unshift()

C) splice()

D) pop()

27 / 30

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

A) Transforms each array element and returns a new array

B) Filters elements based on a condition

C) Mutates the original array

D) Sorts the array

28 / 30

28. What is the purpose of the Blob object?

A) To store cookies.

B) To create HTML elements.

C) To compress data.

D) To represent binary data.

29 / 30

29. What will the following code do? document.getElementById("myDiv").style.color = "red";

A) Change the background color of myDiv to red.

B) Throw an error.

C) Change the text color of myDiv to red.

D) Do nothing.

30 / 30

30. How can you remove an item from localStorage?

A) localStorage.delete()

B) localStorage.clearItem()

C) localStorage.removeItem()

D) localStorage.eraseItem()

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