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 focus event in JavaScript?

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

B) It triggers when an element loses focus.

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

D) It triggers when an element gains focus.

2 / 30

2. What is the main drawback of callbacks?

A) Difficult error handling

B) Poor readability

C) Callback hell (nested callbacks)

D) All of the above

3 / 30

3. 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()

4 / 30

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

A) Using _ as a prefix

B) Using const

C) Using the private keyword

D) Using # as a prefix

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5. What is the purpose of the performance.now() method?

A) To pause code execution.

B) To profile memory usage.

C) To display the current date and time.

D) To measure code execution time in milliseconds with high precision.

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

A) Opens a new browser tab or window.

B) Reloads the current page.

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

D) Closes the current window.

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7. What does const keyword do?

A) Declares a variable that cannot be reassigned

B) Declares a variable with block scope

C) Declares a constant variable with global scope

D) Both B and C

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8. What is the default content type for POST requests in AJAX?

A) text/plain

B) application/json

C) application/x-www-form-urlencoded

D) multipart/form-data

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

A) Decrypts a string.

B) Creates a random number.

C) Generates a unique identifier.

D) Encrypts a string.

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

A) getElementsByTag

B) getElementById

C) getElementByClass

D) querySelector

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

A) Fetches the current page title.

B) Redirects to a new URL.

C) Modifies the browser history without reloading the page.

D) Clears the browser history.

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12. What does the Notification API do?

A) Displays browser notifications.

B) Tracks the user's activity.

C) Sends notifications to the user's email.

D) Updates the webpage title.

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13. What does the this keyword represent inside an object method?

A) The parent object

B) Undefined

C) The global object

D) The object that owns the method

14 / 30

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

A) addListener()

B) attachListener()

C) registerEvent()

D) addEventListener()

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15. What is the main purpose of console.trace() in debugging?

A) To log all variables in scope.

B) To measure execution time.

C) To stop code execution.

D) To display the stack trace of a function call.

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

A) By using await inside the function

B) By adding async before the function name

C) By calling .then() inside the function

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

17 / 30

17. Which of the following is not a JavaScript data type?

A) Boolean

B) Float

C) String

D) Number

18 / 30

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

A) Resolves with the fastest promise

B) Resolves with all promises' results

C) Rejects all promises if one fails

D) Pauses until all promises are complete

19 / 30

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

A) All of the above.

B) Minify and compress files.

C) Scan for vulnerabilities using automated tools.

D) Perform thorough testing.

20 / 30

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

A) WebSockets

B) DOMParser

C) Event API

D) Fetch API

21 / 30

21. What does DOM stand for in JavaScript?

A) Data Object Model

B) Dynamic Object Model

C) Document Oriented Model

D) Document Object Model

22 / 30

22. What will the output of console.log(0.1 + 0.2 === 0.3);?

A) It throws an error.

B) false

C) true

D) undefined

23 / 30

23. Which DevTools feature helps analyze how long each function takes to execute?

A) Application tab

B) Network tab

C) Console

D) Performance tab

24 / 30

24. What is asynchronous JavaScript?

A) Code executed without using variables

B) Code executed in parallel without blocking

C) Code executed line by line in order

D) Code executed only after page load

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25. How do you toggle a class on an element?

A) element.classList.toggle(className)

B) element.toggle(className)

C) element.switchClass(className)

D) element.classToggle(className)

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

A) wait()

B) testAsync()

C) expectAsync()

D) done()

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27. What does Object.create() do?

A) Creates a new object with the specified prototype

B) Returns a stringified version of an object

C) Creates a deep clone of an object

D) Copies an object

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

A) To improve code readability.

B) To reduce code execution time.

C) To simplify database queries.

D) To prevent SQL Injection attacks.

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

A) To stop animations.

B) To reload the page.

C) To create animations.

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

30 / 30

30. Which operator is used to check equality of value and type?

A) ===

B) !=

C) ==

D) =

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