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

A) document.createElement()

B) document.addElement()

C) document.newElement()

D) document.generateElement()

2 / 30

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

A) clearChild()

B) deleteChild()

C) removeElement()

D) removeChild()

3 / 30

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

A) Stops the execution of the event handler.

B) Stops the event from propagating.

C) Prevents the default action of the event.

D) Removes the event listener.

4 / 30

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

A) To fetch browser settings.

B) To make HTTP requests.

C) To fetch cookies.

D) To fetch local files.

5 / 30

5. What does Object.assign() do?

A) Copies values from one object to another

B) Creates an object reference

C) Merges two arrays

D) Declares an object

6 / 30

6. Which method sends the AJAX request?

A) process()

B) trigger()

C) send()

D) execute()

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. What does the window.location object represent?

A) The browser's settings.

B) The user's geolocation.

C) The browser's history.

D) The URL of the current document.

9 / 30

9. 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

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10. What is the purpose of the Secure flag in cookies?

A) To allow cookies to be accessed over HTTP.

B) To restrict cookies to HTTPS connections only.

C) To encrypt cookie data.

D) To prevent cookies from expiring.

11 / 30

11. Which of these is NOT asynchronous in JavaScript?

A) for loop

B) fetch()

C) Promise.all()

D) setTimeout()

12 / 30

12. What does the static keyword do in a class?

A) Defines a method accessible only on the class itself, not instances

B) Creates a constant variable

C) Creates an instance of a class

D) Makes a property immutable

13 / 30

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

A) Embed them in the HTML file.

B) Store them in local storage.

C) Store them in plain text files.

D) Store them in the backend server.

14 / 30

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

A) define

B) object

C) class

D) new

15 / 30

15. What does the Promise constructor accept?

A) An array of values

B) Another promise

C) A callback function with resolve and reject parameters

D) A string argument

16 / 30

16. What is event bubbling in JavaScript?

A) Events that do not propagate.

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

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

D) Events triggering only on the target element.

17 / 30

17. What does the filter() method do?

A) Filters elements based on a condition

B) Transforms array elements

C) Removes duplicates from an array

D) Mutates the original array

18 / 30

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

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

B) A method for improving performance.

C) A browser feature to cache data.

D) A rule to prevent HTTP requests.

19 / 30

19. What is the difference between stopPropagation() and preventDefault()?

A) Both stop the event from propagating.

B) Both prevent the default behavior.

C) stopPropagation() stops event bubbling, while preventDefault() stops the default action.

D) There is no difference.

20 / 30

20. 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.

21 / 30

21. What is the purpose of Object.getPrototypeOf()?

A) To seal an object

B) To modify an object's prototype

C) To create a prototype for an object

D) To retrieve the prototype of an object

22 / 30

22. Which method is used to handle promises in JavaScript?

A) then

B) finally

C) All of the above

D) catch

23 / 30

23. How do you check the status of an AJAX request?

A) responseCode

B) readyState

C) status

D) statusCode

24 / 30

24. What is polymorphism in JavaScript?

A) Creating multiple instances of a class

B) Inheriting properties from multiple classes

C) None of the above

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

25 / 30

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

A) Redirect behavior

B) Cache policy

C) Request timeout

D) Include cookies in requests

26 / 30

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

A) addEventListener()

B) addListener()

C) registerEvent()

D) attachListener()

27 / 30

27. How do you handle errors in the Fetch API?

A) Using onerror

B) Using try...catch

C) Using then()

D) Using a catch() block

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28. What does Promise.resolve() do?

A) Waits for a promise to resolve

B) Resolves a pending promise with a given value

C) Creates a pending promise

D) Rejects a promise

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

A) Pauses until all promises are complete

B) Rejects all promises if one fails

C) Resolves with the fastest promise

D) Resolves with all promises' results

30 / 30

30. Which type of data should never be stored in client-side storage like localStorage?

A) API keys

B) Non-sensitive data

C) Caching information

D) User preferences

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