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 operator is used to check equality of value and type?

A) ===

B) =

C) !=

D) ==

2 / 30

2. What is JavaScript primarily used for?

A) Writing system-level software

B) Designing static websites

C) Adding interactivity to web pages

D) Server-side programming

3 / 30

3. Which new feature was introduced in ES6 for iteration?

A) while

B) do...while

C) forEach

D) for...of

4 / 30

4. What is a potential risk of using inline JavaScript?

A) Increased file size.

B) Difficulty in debugging.

C) Reduced performance.

D) Exposure to XSS attacks.

5 / 30

5. What is the purpose of reduce() in JavaScript?

A) Concatenates arrays

B) Executes a reducer function on each element, resulting in a single output

C) Reduces array size

D) Filters elements

6 / 30

6. What is the default HTTP method used by AJAX?

A) DELETE

B) PUT

C) GET

D) POST

7 / 30

7. How can you make a function return a promise in ES6?

A) By using await inside the function

B) By wrapping the return value in Promise.resolve()

C) By calling .then() inside the function

D) By adding async before the function name

8 / 30

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

A) element.createAttribute(name, value)

B) element.setAttribute(name, value)

C) element.addAttribute(name, value)

D) element.attribute(name, value)

9 / 30

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

A) deleteChild()

B) removeElement()

C) removeChild()

D) clearChild()

10 / 30

10. Which method is used to trigger a custom event?

A) fireEvent()

B) triggerEvent()

C) dispatchEvent()

D) emitEvent()

11 / 30

11. Which of the following is not a valid JavaScript variable name?

A) name2

B) 2name

C) _name

D) $name

12 / 30

12. How do you define a private field in a class?

A) Using # as a prefix

B) Using the private keyword

C) Using _ as a prefix

D) Using const

13 / 30

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

A) unshift()

B) push()

C) splice()

D) pop()

14 / 30

14. What is the purpose of async in JavaScript?

A) Returns multiple promises

B) Converts a promise into a callback

C) Makes a function asynchronous

D) Pauses function execution

15 / 30

15. What does the rest parameter (...) do?

A) Expands arrays into individual elements

B) Creates an object

C) Declares optional arguments

D) Condenses multiple arguments into an array

16 / 30

16. What is the primary purpose of unit testing?

A) To test the entire application workflow.

B) To identify security vulnerabilities.

C) To test individual components or functions.

D) To measure application performance.

17 / 30

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

A) Rejects all promises if one fails

B) Resolves with all promises' results

C) Resolves with the fastest promise

D) Pauses until all promises are complete

18 / 30

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

A) JSON.toJSON()

B) JSON.convert()

C) JSON.stringify()

D) JSON.parse()

19 / 30

19. What does await do in an async function?

A) Resolves a promise

B) Pauses the execution until the promise resolves

C) Creates a promise

D) Rejects a promise

20 / 30

20. What happens if you call stopPropagation() inside a capturing phase listener?

A) The event continues in the bubbling phase.

B) The event is ignored entirely.

C) The event propagation stops completely.

D) Only the target element receives the event.

21 / 30

21. What does the filter() method do?

A) Removes duplicates from an array

B) Transforms array elements

C) Mutates the original array

D) Filters elements based on a condition

22 / 30

22. Which AJAX technique updates only parts of a web page?

A) DOM parsing

B) Lazy loading

C) Page refresh

D) Partial rendering

23 / 30

23. Why should third-party libraries be used cautiously?

A) They are harder to debug.

B) They might contain vulnerabilities or malicious code.

C) They reduce code size.

D) They always introduce compatibility issues.

24 / 30

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

A) Both B and C

B) let newArr = oldArr.slice();

C) let newArr = oldArr;

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

25 / 30

25. What is lazy loading in performance optimization?

A) Minimizing HTTP requests.

B) Preloading all images in the background.

C) Loading all assets upfront.

D) Delaying loading of resources until they are needed.

26 / 30

26. What is the purpose of the splice() method?

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

B) To add elements to an array.

C) To remove elements from an array.

D) None of the above.

27 / 30

27. Which method is used to select an element by its ID in JavaScript?

A) querySelector

B) getElementById

C) getElementByClass

D) getElementsByTag

28 / 30

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

A) To set the request headers

B) To define the status code of the response

C) To define the format of the response

D) To define the method used in the request

29 / 30

29. What does AJAX stand for?

A) Advanced JavaScript and XHTML

B) Asynchronous Java and XML

C) Asynchronous JavaScript and XML

D) Asynchronous JSON and XML

30 / 30

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

A) expectAsync()

B) testAsync()

C) wait()

D) done()

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