JavaScript Quiz Test Online (30 random Questions) 2025

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 does the includes() method do in ES6?

A) Checks if an array contains a specified value

B) Works on both arrays and strings

C) All of the above

D) Checks if a string contains a substring

2 / 30

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

A) It does not modify the resolved value.

B) It executes after the promise is settled.

C) It runs only on a rejected promise.

D) It can be used for cleanup.

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3. What does the window.scrollTo() method do?

A) Highlights the content on the page.

B) Scrolls the document to a specific position.

C) Adjusts the browser zoom level.

D) Saves the current scroll position.

4 / 30

4. What is JSONP in the context of AJAX?

A) A replacement for XMLHttpRequest

B) A method to fetch JSON data from other domains

C) A modern AJAX API

D) A JSON parser for browsers

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5. What should you do before deploying a JavaScript application?

A) All of the above.

B) Minify and compress files.

C) Perform thorough testing.

D) Scan for vulnerabilities using automated tools.

6 / 30

6. What does the IntersectionObserver API do?

A) Tracks visibility of elements within the viewport.

B) Observes changes to DOM nodes.

C) Observes HTTP requests.

D) Monitors resizing of elements.

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7. Which response type is used to receive data as JSON?

A) blob

B) text

C) json

D) xml

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8. How can developers avoid exposing sensitive information in source maps?

A) Store source maps in cookies.

B) Avoid debugging tools.

C) Use unminified files.

D) Disable source maps in production.

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9. Which method is used to open a request in XMLHttpRequest?

A) openRequest()

B) start()

C) open()

D) beginRequest()

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

A) A method for secure data encryption.

B) A technique to improve web application performance.

C) A technique for caching web pages.

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

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11. Which method is used to test asynchronous code in Jest?

A) done()

B) expectAsync()

C) wait()

D) testAsync()

12 / 30

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

A) To stop animations.

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

C) To create animations.

D) To reload the page.

13 / 30

13. How do you detect which key was pressed during a keydown event?

A) event.which

B) event.key

C) event.code

D) All of the above

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14. What is Cross-Site Request Forgery (CSRF)?

A) An attack that steals cookies.

B) A vulnerability in JavaScript frameworks.

C) A type of browser exploit.

D) An attack where unauthorized commands are executed on behalf of an authenticated user.

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

A) To destroy an object

B) To define methods

C) To initialize properties when an object is created

D) To inherit another class

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16. Why is it important to use parameterized queries in JavaScript?

A) To prevent SQL Injection attacks.

B) To simplify database queries.

C) To improve code readability.

D) To reduce code execution time.

17 / 30

17. Which of the following methods is used to convert a JavaScript object to JSON format?

A) JSON.stringify()

B) JSON.parse()

C) JSON.convert()

D) JSON.toJSON()

18 / 30

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

A) NaN

B) null

C) undefined

D) 0

19 / 30

19. Which of the following methods removes all child nodes of a DOM element?

A) element.removeChildren()

B) element.deleteChildren()

C) element.innerHTML = ""

D) element.clear()

20 / 30

20. What does the HttpOnly flag on cookies do?

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

B) Ensures cookies can only be accessed by JavaScript.

C) Extends the lifespan of cookies.

D) Encrypts cookie data.

21 / 30

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

A) parent();

B) super();

C) constructor();

D) base();

22 / 30

22. What is the default state of a JavaScript promise?

A) Pending

B) Fulfilled

C) Rejected

D) Resolved

23 / 30

23. How can you monitor memory usage in a web application?

A) Using the Memory tab in DevTools.

B) By enabling verbose logging.

C) Using the Console tab in DevTools.

D) By writing custom JavaScript functions.

24 / 30

24. Which symbol is used to create private class fields in ES6+?

A) #

B) @

C) private keyword

D) _

25 / 30

25. What happens if await is used outside an async function?

A) It throws an error

B) It skips the await keyword

C) It resolves the promise automatically

D) It works normally

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26. How can you add a new child element to an existing DOM element?

A) addChild()

B) insertChild()

C) appendChild()

D) createChild()

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27. What does DOM stand for in JavaScript?

A) Document Object Model

B) Dynamic Object Model

C) Document Oriented Model

D) Data Object Model

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28. How does Object.entries() work in ES6?

A) Returns an array of key-value pairs from an object

B) Merges two objects

C) Creates an object clone

D) Converts an object into a string

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

A) element.attachEvent()

B) element.bindEvent()

C) element.onEvent()

D) element.addEventListener()

30 / 30

30. What is the default phase of event propagation?

A) Bubbling phase

B) None of the above

C) Target phase

D) Capturing phase

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