Java Interview Questions

JavaScript Interview Questions and Answers

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JavaScript is one of the most popular programming languages in the world and a core technology for web development. As a result, JavaScript interview questions frequently come up in tech job interviews, testing a candidate’s knowledge of JavaScript fundamentals, APIs, asynchronous programming, and more.

In this complete guide, we have compiled the most common and important JavaScript interview questions to help you prepare for your upcoming interview.

Basic JavaScript Interview Questions

JavaScript is a lightweight, interpreted programming language that runs in any browser. Here are some common basic interview questions on core JavaScript:

What are the different data types in JavaScript?

The latest ECMAScript standard defines seven data types in JavaScript:

  • Primitive data types:
    • Number – for numbers like 100, 3.14 etc.
    • String – for strings of text e.g. “Hello”
    • Boolean – for true/false values
    • Null – a null value
    • Undefined – a variable declared but no value assigned
    • Symbol – data type whose instances are unique
  • Non-primitive data type:
    • Object – for more complex data structures like arrays, dates etc.

What is the difference between null and undefined?

  • Null is an assigned value representing no value. It is an empty value variable defined by a developer.
  • Undefined means a variable has been declared but not defined yet. It is assigned by JavaScript automatically.

What are JavaScript closures?

JavaScript closures allow a function to access variables from an enclosing scope or outer function even after the outer function has closed. This persistence of the function scope/context is called closure in JavaScript.

What is the difference between == and === operators?

  • The equality operator == allows loose equality with type conversion.
  • The strict equality operator === enforces strict equality with no type conversion.

For example:


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console.log(1 == ‘1’); // true

console.log(1 === ‘1’); // false

Intermediate JavaScript Interview Questions

Here are some slightly more advanced JavaScript interview questions and answers on concepts like scoping, inheritance, promises etc:

What is hoisting in JavaScript?

Hoisting in JavaScript allows access to function declarations and variables before they are declared. Variables are hoisted to the top and initialized with a default value of undefined. Function declarations are hoisted completely.

How does prototypal inheritance work in JavaScript?

All JavaScript objects have a hidden [[Prototype]] property that makes inheritance possible in JavaScript. The prototype object contains properties and methods that can be accessed by all instances via the __proto__ property.

When a property is accessed on an object:

  • If the property exists on the object itself, that value is used
  • If not, the JavaScript engine looks down the prototype chain until it finds the property.

What are JavaScript promises?

Promises represent the eventual completion or failure of an asynchronous operation. They provide an alternative approach for asynchronous code handling compared to callbacks.

A promise can be in three states:

  • Pending – initial state
  • Fulfilled – operation completed successfully
  • Rejected – operation failed

Promises avoid callback hell and make asynchronous code look synchronous.

What are classes in JavaScript?

JavaScript classes are templates for creating objects. They provide reuseable code using inheritance, constructors and methods.



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class ClassName {


  constructor() { }


  method1() { }


  method2() { }



Advanced JavaScript Interview Questions

Let’s look at some advanced JS interview questions now:

Explain event delegation

Event delegation allows adding event listeners to a parent element instead of adding them directly to child elements.

The listener on the parent element analyzes bubbled events from descendants to find a match on child elements.


  • Less memory usage
  • Easier to add/remove elements

What is the difference between synchronous and asynchronous code in JavaScript?

Synchronous code is executed in sequence, blocking further execution until completion.

Asynchronous code allows other code to execute while waiting for long-running tasks via callbacks, promises, async/await etc.

Asynchronous programming avoids blocking and improves performance of web apps.

What are common memory leaks in JavaScript?

Some common memory leaks:

  • Global variables holding unwanted references to objects
  • Event listeners not removed after use
  • Outdated references to DOM nodes after removal
  • Cached references in closures

These continue to occupy memory though no longer required.

What is memoization in JavaScript?

Memoization is the process of caching the output of expensive function calls to avoid repeated computations on same inputs.

This technique is commonly used for optimizing recursive functions.

JavaScript Coding Interview Questions

Some sample coding problems you may encounter:



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// Print numbers from 1 to 100

// For multiples of 3 print “Fizz” instead of number

// For multiples of 5 print “Buzz”

// For multiples of 3 and 5 print “FizzBuzz”

Palindrome Checker


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function isPalindrome(str) {


  // Remove spaces, lowercase 

  str = str.replace(/\s/g, “”).toLowerCase();


  // Check if str is equal to reverse of str

  return str === str.split(“”).reverse().join(“”); 



Fibonacci Series Generator


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function fibonacci(n) {


  // Base case

  if (n <= 1) return n;


  return fibonacci(n1) + fibonacci(n2);




This covers the most important JavaScript interview questions and answers for both freshers and experienced developers.

Key topics include data types, closures, prototypes, promises, async/await, DOM manipulation and more.

Practice these questions thoroughly so you can confidently answer them during interviews. Keep learning more advanced JavaScript concepts to take your skills to the next level.

Best of luck with your JavaScript job interview!

Your Gateway to High Domain Authority Guest Posting

In the vast digital landscape, where information reigns supreme, the need for a platform that empowers individuals and businesses to share their stories is crucial. emerges as a beacon in this realm, offering a free guest posting service with a remarkable Domain Authority (DA) of 50. In this article, we will delve into the significance of, exploring its features, benefits, and the opportunities it presents for content creators and marketers.

I. Understanding is a user-friendly platform that caters to the growing demand for high-quality guest posting. Its impressive Domain Authority of 50 signifies its credibility and influence in the online space. DA is a metric developed by Moz that predicts how well a website will rank on search engine result pages (SERPs). A higher DA indicates a stronger online presence, making an attractive platform for those seeking visibility.

II. Features of

  1. Free Guest Posting: One of the most appealing aspects of is its commitment to providing a free guest posting service. This democratizes the content creation process, allowing individuals and businesses of all sizes to share their perspectives without any financial barriers.

  2. High Domain Authority (DA 50): The DA of 50 places among the top-tier websites in terms of authority. This not only enhances the visibility of the content posted on the platform but also contributes to better search engine rankings. For content creators and marketers, this is a golden opportunity to tap into a platform that has already established its credibility.

  3. User-Friendly Interface: boasts a user-friendly interface that simplifies the submission process. Whether you are a seasoned content creator or a novice, the platform ensures a smooth and hassle-free experience, allowing you to focus on crafting compelling content.

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  5. SEO Benefits: Leveraging the high Domain Authority of can significantly impact your website's SEO. Backlinks from authoritative sites play a crucial role in search engine algorithms, and by contributing content to, you have the opportunity to acquire valuable backlinks that can enhance your website's visibility.

III. The Benefits of Guest Posting on

  1. Enhanced Visibility: Submitting content to a platform with a DA of 50 opens the door to a broader audience. Your content is more likely to be discovered by users actively seeking information in your niche, contributing to increased visibility for your brand or personal brand.

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  4. SEO Boost: Backlinks from high-authority sites are a powerful SEO tool. By contributing to, you can improve your website's SEO performance, leading to better rankings on search engines and increased organic traffic.

IV. How to Get Started with

  1. Create an Account: To begin your guest posting journey on, create an account on the platform. This will give you access to the submission process and other features offered by the site.

  2. Choose a Relevant Category: Select the category that aligns with the content you want to share. This ensures that your content reaches the right audience and fits seamlessly into the platform's diverse ecosystem.

  3. Craft Compelling Content: The success of your guest post depends on the quality of your content. Craft a well-researched, engaging, and informative piece that adds value to the readers and reflects positively on your expertise.

  4. Follow Submission Guidelines: Each platform has its own set of guidelines for guest submissions. Pay close attention to's guidelines to ensure that your content meets the platform's standards. This includes formatting, word count, and any specific requirements outlined by the site.

  5. Utilize the Author Bio Section: Don't overlook the author bio section when submitting your content. This is an opportunity to introduce yourself to the audience and include relevant links to your website or social media profiles, further enhancing your online presence.

Frequently Asked Questions (FAQs):

Q1: Is guest posting on completely free?

Yes, offers a free guest posting service, eliminating any financial barriers for individuals and businesses looking to share their content.

Q2: How can I benefit from the high Domain Authority of

The high Domain Authority of contributes to better search engine rankings and increased visibility. By contributing quality content, you can leverage this authority to enhance your own website's SEO performance.

Q3: Are there specific guidelines for guest submissions on

Yes, has specific guidelines for guest submissions. It is essential to carefully review and adhere to these guidelines, ensuring your content meets the platform's standards.

Q4: Can I include links to my website or social media profiles in the guest post?

Yes, the author bio section in your guest post submission is an opportunity to include relevant links to your website or social media profiles, enhancing your online presence.

Q5: How can I connect with other content creators on

Guest posting on not only allows you to share your content but also provides a platform for networking. Engage with other contributors, businesses, and thought leaders to explore collaboration opportunities and increase your exposure.

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