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 HttpOnly flag on cookies do?

A) Ensures cookies can only be accessed by JavaScript.

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

C) Extends the lifespan of cookies.

D) Encrypts cookie data.

2 / 30

2. What is the primary purpose of Content Security Policy (CSP)?

A) To prevent unauthorized file downloads.

B) To mitigate XSS attacks by controlling resources a browser can load.

C) To restrict API usage in JavaScript.

D) To enforce HTTPS.

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

A) PUT

B) POST

C) GET

D) DELETE

4 / 30

4. What is the main drawback of callbacks?

A) Callback hell (nested callbacks)

B) Poor readability

C) All of the above

D) Difficult error handling

5 / 30

5. What is the purpose of a nonce attribute in a CSP?

A) To encrypt inline scripts.

B) To allow specific inline scripts to execute securely.

C) To block all external scripts.

D) To prevent HTTP requests.

6 / 30

6. Why should eval() be avoided in JavaScript?

A) It is outdated.

B) It doesn't work with modern browsers.

C) It can introduce security vulnerabilities like XSS.

D) It reduces performance.

7 / 30

7. What is the purpose of the Blob object?

A) To represent binary data.

B) To compress data.

C) To create HTML elements.

D) To store cookies.

8 / 30

8. Which of the following is NOT a valid DOM event?

A) hover

B) click

C) mouseover

D) change

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9. How do you handle errors in an async function?

A) Using finally

B) Using catch

C) Using try...catch

D) None of the above

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10. JavaScript is a _______ language.

A) Assembly-level

B) Interpreted

C) Low-level

D) Compiled

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11. What type of data is commonly used in an AJAX response?

A) Plain text

B) All of the above

C) JSON

D) XML

12 / 30

12. What does the Promise constructor accept?

A) A string argument

B) Another promise

C) An array of values

D) A callback function with resolve and reject parameters

13 / 30

13. 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) Filters elements

D) Reduces array size

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14. Which statement correctly defines a function in JavaScript?

A) fun myFunction() {}

B) function myFunction() {}

C) function: myFunction() {}

D) def myFunction() {}

15 / 30

15. How do you ensure a function runs only after a specific promise is resolved?

A) Use Promise.reject.

B) Use setTimeout.

C) Use .then() or await.

D) Use a synchronous loop.

16 / 30

16. What will the following code do? document.getElementById("myDiv").style.color = "red";

A) Change the text color of myDiv to red.

B) Do nothing.

C) Throw an error.

D) Change the background color of myDiv to red.

17 / 30

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

A) Check the navigator.cookieEnabled property.

B) Access the cookieStore API.

C) Use the document.cookies property.

D) Call checkCookies() method.

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18. What type of attack is prevented by using the X-Frame-Options header?

A) phishing

B) injection

C) clickjacking

D) sniffing

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

A) Opens a new browser tab or window.

B) Closes the current window.

C) Reloads the current page.

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

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20. What does the target property of an event object return?

A) The default action of the event.

B) The parent element of the event.

C) The element that triggered the event.

D) The type of the event.

21 / 30

21. What is the output of console.log(1 + "2" + 3);?

A) 6

B) "6"

C) "123"

D) 33

22 / 30

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

A) setTimeout()

B) executeLater()

C) setRepeater()

D) setInterval()

23 / 30

23. What is the primary use of strict mode in JavaScript?

A) To enhance security by catching common coding errors.

B) To prevent API misuse.

C) To optimize performance.

D) To enforce HTTPS.

24 / 30

24. What is the purpose of the focus event in JavaScript?

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

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

C) It triggers when an element gains focus.

D) It triggers when an element loses focus.

25 / 30

25. What does Promise.resolve() do?

A) Creates a pending promise

B) Rejects a promise

C) Waits for a promise to resolve

D) Resolves a pending promise with a given value

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26. What is the difference between call() and apply() methods in JavaScript?

A) Both are used to create new objects.

B) apply() accepts arguments as an array, call() as separate arguments.

C) call() accepts arguments as an array, apply() as separate arguments.

D) Both are the same in functionality.

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27. What is the default phase of event propagation?

A) None of the above

B) Capturing phase

C) Target phase

D) Bubbling phase

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28. What does the let keyword do in ES6?

A) Declares a variable with function scope

B) Declares a variable with block scope

C) Declares a variable globally

D) Declares a constant variable

29 / 30

29. 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) <script href="script.js"></script>

D) <javascript src="script.js"></javascript>

30 / 30

30. Which of the following is a common cause of memory leaks in JavaScript?

A) Event listeners not being removed.

B) Using arrow functions.

C) Using const instead of var.

D) Unreferenced closures.

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