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

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

A) To measure execution time.

B) To stop code execution.

C) To log all variables in scope.

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

2 / 30

What is the purpose of Promise.all()?

A) Resolves multiple promises concurrently

B) Creates a single promise

C) Rejects all promises if one fails

D) Resolves multiple promises sequentially

3 / 30

Which keyword is used to define a constant in JavaScript?

A) constant

B) const

C) let

D) var

4 / 30

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

A) createChild()

B) appendChild()

C) insertChild()

D) addChild()

5 / 30

What does Object.assign() do?

A) Merges two arrays

B) Creates an object reference

C) Declares an object

D) Copies values from one object to another

6 / 30

Which of the following is NOT a valid DOM event?

A) mouseover

B) hover

C) click

D) change

7 / 30

What is event bubbling in JavaScript?

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

B) Events triggering only on the target element.

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

D) Events that do not propagate.

8 / 30

What is the use of arrow functions in ES6?

A) All of the above

B) Declares functions with lexical this binding

C) Supports this context binding

D) Declares functions with a simpler syntax

9 / 30

What is the default state of a JavaScript promise?

A) Pending

B) Resolved

C) Rejected

D) Fulfilled

10 / 30

How do you check the status of an AJAX request?

A) responseCode

B) readyState

C) statusCode

D) status

11 / 30

What is Cross-Site Scripting (XSS)?

A) A technique for caching web pages.

B) A technique to improve web application performance.

C) A method for secure data encryption.

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

12 / 30

How can you handle both the response and errors in the Fetch API?

A) Using catch() only

B) Using then() only

C) Using finally()

D) Using then() and catch()

13 / 30

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

A) Using const instead of var.

B) Unreferenced closures.

C) Using arrow functions.

D) Event listeners not being removed.

14 / 30

How can you write a comment in JavaScript?

A)

B) /$ This is a comment $/

C) /* This is a comment */

D) # This is a comment

15 / 30

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

A) document.addElement()

B) document.newElement()

C) document.generateElement()

D) document.createElement()

16 / 30

What is a potential risk of using inline JavaScript?

A) Reduced performance.

B) Increased file size.

C) Exposure to XSS attacks.

D) Difficulty in debugging.

17 / 30

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

A) application/json

B) application/x-www-form-urlencoded

C) text/plain

D) multipart/form-data

18 / 30

What does the navigator.geolocation.getCurrentPosition() method do?

A) Updates the user's address.

B) Retrieves the user's current location.

C) Sets the user's location.

D) Fetches the current time.

19 / 30

Which function repeatedly executes code after a set interval?

A) setRepeater()

B) setInterval()

C) setTimeout()

D) executeLater()

20 / 30

Which method in Chrome DevTools helps measure script execution time?

A) console.log()

B) performance.now()

C) debugger

D) console.time() and console.timeEnd()

21 / 30

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

A) To restrict API usage in JavaScript.

B) To enforce HTTPS.

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

D) To prevent unauthorized file downloads.

22 / 30

How can CSRF attacks be mitigated?

A) By implementing CSRF tokens.

B) By validating user inputs.

C) By using strong passwords.

D) By disabling cookies.

23 / 30

Which method sends the AJAX request?

A) trigger()

B) process()

C) execute()

D) send()

24 / 30

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

A) base();

B) super();

C) constructor();

D) parent();

25 / 30

Which API is used to measure page load times?

A) Performance API

B) MediaStream API

C) Web Animations API

D) Event Loop API

26 / 30

What is method overriding in JavaScript?

A) Calling a method multiple times

B) Changing the return type of a method

C) A subclass providing its own implementation of a method inherited from a parent class

D) Defining multiple methods with the same name

27 / 30

What happens when a return statement is used inside a forEach loop?

A) It throws an error.

B) It exits the function containing the loop.

C) It skips to the next iteration.

D) The loop stops.

28 / 30

What is asynchronous JavaScript?

A) Code executed in parallel without blocking

B) Code executed line by line in order

C) Code executed without using variables

D) Code executed only after page load

29 / 30

Which statement correctly defines a function in JavaScript?

A) function myFunction() {}

B) def myFunction() {}

C) fun myFunction() {}

D) function: myFunction() {}

30 / 30

What is the purpose of async in JavaScript?

A) Converts a promise into a callback

B) Returns multiple promises

C) Makes a function asynchronous

D) Pauses function execution

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