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 the purpose of the splice() method?

A) None of the above.

B) To add elements to an array.

C) To remove elements from an array.

D) To remove and/or add elements to an array.

2 / 30

2. Which feature allows you to create computed property names in objects?

A) Square brackets ([])

B) Template literals

C) Object.assign()

D) Arrow functions

3 / 30

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

A) executeLater()

B) setRepeater()

C) setTimeout()

D) setInterval()

4 / 30

4. What does the filter() method do?

A) Transforms array elements

B) Filters elements based on a condition

C) Mutates the original array

D) Removes duplicates from an array

5 / 30

5. What is a Same-Origin Policy (SOP)?

A) A rule to prevent HTTP requests.

B) A method for improving performance.

C) A policy restricting how scripts interact with content from different origins.

D) A browser feature to cache data.

6 / 30

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

A) Performance API

B) MediaStream API

C) Event Loop API

D) Web Animations API

7 / 30

7. What is the purpose of a constructor in a class?

A) To inherit another class

B) To initialize properties when an object is created

C) To destroy an object

D) To define methods

8 / 30

8. What does the IntersectionObserver API do?

A) Observes changes to DOM nodes.

B) Observes HTTP requests.

C) Tracks visibility of elements within the viewport.

D) Monitors resizing of elements.

9 / 30

9. What is the prototype in JavaScript?

A) A way to destroy objects

B) A method for copying objects

C) A keyword for creating objects

D) A mechanism to inherit properties and methods

10 / 30

10. Which method is used to create a shallow copy of an array in ES6?

A) Array.clone()

B) [...array]

C) Array.copy()

D) Array.prototype.copy()

11 / 30

11. What is the primary purpose of unit testing?

A) To test the entire application workflow.

B) To test individual components or functions.

C) To measure application performance.

D) To identify security vulnerabilities.

12 / 30

12. What does the HttpOnly flag on cookies do?

A) Encrypts cookie data.

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

C) Ensures cookies can only be accessed by JavaScript.

D) Extends the lifespan of cookies.

13 / 30

13. Which of these is an example of an asynchronous task in AJAX?

A) Page reload

B) Form submission

C) File download

D) Data fetching from a server

14 / 30

14. What is the purpose of the Coverage tab in Chrome DevTools?

A) To identify unused CSS and JavaScript.

B) To debug event listeners.

C) To display memory usage.

D) To measure network requests.

15 / 30

15. Which feature allows default values in functions?

A) Arrow functions

B) Rest parameters

C) Default parameters

D) Spread operator

16 / 30

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

A) validate

B) hash

C) parse

D) sanitize

17 / 30

17. What is the purpose of using try...catch blocks in debugging?

A) To log error messages to the console.

B) To catch and handle runtime errors gracefully.

C) To prevent syntax errors.

D) To improve application performance.

18 / 30

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

A) obj.property

B) Both A and C

C) obj.hasOwnProperty(property)

D) property in obj

19 / 30

19. What does the preventDefault() method do in an event handler?

A) Stops the event from propagating.

B) Prevents the default action of the event.

C) Stops the execution of the event handler.

D) Removes the event listener.

20 / 30

20. What is JSONP in the context of AJAX?

A) A modern AJAX API

B) A replacement for XMLHttpRequest

C) A method to fetch JSON data from other domains

D) A JSON parser for browsers

21 / 30

21. How do you prevent the default form submission in AJAX?

A) By calling event.stopPropagation()

B) By using form.submit()

C) By setting method="get"

D) By calling event.preventDefault()

22 / 30

22. What does the let keyword do in ES6?

A) Declares a variable with function scope

B) Declares a constant variable

C) Declares a variable with block scope

D) Declares a variable globally

23 / 30

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

A) The time since the browser was opened.

B) The time since the page started loading.

C) The current time in milliseconds.

D) The user's system time.

24 / 30

24. Which keyword is used to stop a loop in JavaScript?

A) end

B) exit

C) stop

D) break

25 / 30

25. 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

26 / 30

26. How can you detect if cookies are enabled in the browser?

A) Call checkCookies() method.

B) Access the cookieStore API.

C) Use the document.cookies property.

D) Check the navigator.cookieEnabled property.

27 / 30

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

A) Closes the connection

B) Cancels an ongoing request

C) Logs errors in the request

D) Resends the request

28 / 30

28. 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>

29 / 30

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

A) Local storage

B) Encrypted cookies with HttpOnly and Secure flags

C) Cookies without flags

D) Plain JavaScript variables

30 / 30

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

A) Modifies the browser history without reloading the page.

B) Clears the browser history.

C) Redirects to a new URL.

D) Fetches the current page title.

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