Latest Top 20 Javascript Interview Questions and Answers for Freshers

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Are you a JavaScript developer looking to land a job at one of the top US multinational companies (MNCs)? Or maybe you’re a recruiter from a leading US MNC searching for the perfect JavaScript developer? Either way, you’ve come to the right place! This guide will discuss top JavaScript interview questions and answers to help you either secure your dream job or find the ideal candidate with ease.

With expert tips and easy-to-understand explanations, this collection will save you time and effort while boosting your chances of success. So, let’s dive in and discover how to ace your next interview or hire the best JavaScript developer!

Basic Introduction to Javascript

Brendan Eich created JavaScript in 1995, which is one of the most popular programming languages for web development. Initially, it was designed to create dynamic web pages. A JavaScript program also called a script, can add to the HTML of any web page and runs automatically when the page loads. Over time, JavaScript has evolved significantly. Now, it can run on web browsers, servers, and almost any device with a JavaScript Engine.

After HTML and CSS, JavaScript is considered the third core technology for web development. It’s a versatile scripting language used for creating websites, mobile apps, web servers, games, and much more. Since JavaScript is object-oriented, it’s perfect for building interactive and functional websites and applications.

While JavaScript was originally made to run in browsers, modern advancements like Node.js allow developers to use it on servers as well. In short, you can create web and mobile apps, real-time applications, streaming platforms, and even video games with JavaScript. Additionally, JavaScript frameworks and libraries, such as React and Angular, help developers save time by providing pre-written code for repetitive tasks. This allows them to focus more on building features and delivering high-quality applications efficiently. 

Top 20 Javascript Interview Questions and Answers

Here are some common JavaScript interview questions for freshers to help them prepare for a front-end development role. Practicing these will boost your chances of acing the interview and securing your dream job.

1. What’s the Difference Between JavaScript and Java?

While both Java and JavaScript share similar names, they are, in fact, completely different technologies with unique purposes. To help you better understand their differences, we have clarified your question.

Java

Java is a powerful object-oriented programming language. It is used to build robust applications and is especially known for its cross-platform compatibility. Moreover, with the virtual machine platform, Java allows developers to write code once and run it on almost any device. 

JavaScript

On the other hand, JavaScript is a lightweight scripting language specifically designed for creating interactive and dynamic web pages. Unlike Java, JavaScript can update and manipulate HTML elements in real-time, making websites more engaging and user-friendly. 

In conclusion, while Java is ideal for building large-scale applications, JavaScript excels at adding interactivity to web pages. Both are incredibly useful; however, they serve completely different purposes.

This concept is crucial to prepare for JavaScript interview questions and answers.

2. What are the Different Data Types Used in JavaScript?

Here are the different types of data that JavaScript supports. Understanding these will help you write better and more efficient code:

• Boolean is used for values that are either true or false.
• Null represents an empty or unknown value.
• Undefined is for variables that have been declared but not yet assigned a value.
• The number includes all numerical values, like integers and decimals (floating-point numbers).
• Strings are used to represent text, including characters and alphanumeric values.
• Objects are used for collections of data or more complex values.
• Symbols are unique identifiers that can be used for object properties.

By using these data types effectively, you can manage your data and code in a more organized way. 

3. Why Is JavaScript a Powerful Programming Language?

Here are some key features of JavaScript that make it such a popular choice for developers. Moving ahead, we will let you know some important Javascript interview questions. 

• Lightweight and Interpreted: JavaScript is a lightweight programming language that is easy to use and doesn’t require heavy resources. Plus, it’s interpreted, so it runs directly in the browser without needing to be compiled.
• Cross-Platform Compatibility: It works seamlessly across different platforms and browsers, making it incredibly versatile.
• Open-Source: JavaScript is open-source, meaning anyone can use, modify, and share it freely. Moreover, it fosters a large community of developers.
• Object-Oriented: It supports object-oriented programming principles, allowing you to create reusable and organized code.
• Integration-Friendly: JavaScript integrates effortlessly with both backend and frontend technologies. In addition, it enables developers to build full-stack applications with ease.
• Ideal for Network-Based Applications: It’s especially well-suited for developing interactive, network-based applications, such as web and mobile apps.

With these features, JavaScript continues to be a go-to choice for developers working on a wide range of projects. 

4. How to Create Objects in JavaScript?

JavaScript is a programming language that is designed to work with objects. Therefore, it's a great tool for building web applications that rely on objects to represent real-world things. As a result, JavaScript encourages developers to use objects in their projects.

const student = {

    name: 'John',

    age: 17

}

Furthermore, we will discuss javascript basic interview questions. 

5. How Can You Create the Array in JavaScript?

To learn how to create an array in JavaScript, follow these steps:

var a = [];

var b = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’];

Further, we will let you know some Javascript interview questions and answers. 

6. What is Variable Scope in JavaScript? Explain the Difference Between Global and Local Scope with Examples.

The scope of a variable determines where it can be used in your JavaScript code. There are two main types of scope:

• Global Scope: Variables declared outside of any function have a global scope. In short, they can access from anywhere in your code.
• Local Scope: Variables declared inside a function have local scope. Moreover, they can only access that function.

By understanding these scopes, you can write cleaner and more efficient JavaScript code. In addition, we will describe JavaScript coding questions and answers.  

7. Explain the ‘this’ keyword in JavaScript.

The “this” keyword is a special keyword in JavaScript that refers to the object that the current code is being executed. In other words, it represents the object that "owns" the code.

For example, it's commonly used in constructors to assign values to object properties. Moreover, this allows you to create objects with specific properties and methods.

8. Is JavaScript Case-Sensitive?

Yes, JavaScript is a case-sensitive language. In short, you need to be careful about the capitalization of keywords, variables, and function names. For example, myVariable is different from MyVariable.

To avoid errors, it's important to be consistent with your capitalization when writing JavaScript code.

Here, we have discussed some basic Javascript interview questions and answers for freshers. 

9. Who Created JavaScript?

Netscape Communications Corporation developed JavaScript. It was originally called LiveScript, but it was later renamed to JavaScript.

10. Can You Pass Anonymous Functions as Arguments?

Yes, you can! In JavaScript, you can create anonymous functions and pass them as arguments to other functions. This is a powerful technique that allows you to create flexible and reusable code. For example, you can define a function that takes another function as an argument and then calls that function inside its body. This is often used in callback functions and higher-order functions. The upcoming section will discuss some Javascript interview questions and answers.

11. Explain == and === in JavaScript

Both == and === are used to compare values in JavaScript. However, they work slightly differently:

• == (Loose Equality): This operator compares values after converting them to the same type. For example, "10" and 10 would be considered equal because JavaScript converts the string "10" to the number 10 before comparing.

• === (Strict Equality): This operator compares both the values and the data types of the operands. If the values and types are the same, it returns true. Otherwise, it returns false.

It's generally recommended to use the strict equality operator (===) to avoid unexpected behavior caused by type coercion.

12. Describe the typeof Operator

The typeof operator is a useful tool in JavaScript for determining the data type of a variable or expression. In essence, it returns a string that indicates the data type. For example, if you have a variable x and you want to know its type, you can use typeof x. This will return a string like "number," "string," "boolean," "object," "undefined," or "function," depending on the value of x.

To summarize, the typeof operator is a simple yet powerful way to check the data type of any value in JavaScript.

13. What is a Prompt Box?

A prompt box is a small window that pops up on a webpage to ask the user for input. In other words, it's a simple way to get information from the user before they continue interacting with the page. For example, a prompt box might ask for a username, password, or a specific piece of information.

Typically, a prompt box includes a text field where the user can type their input, a label to explain what kind of input is expected, and two buttons: "OK" to submit the input and "Cancel" to close the box without submitting.

14. How to Effectively Debug JavaScript Code?

Debugging is a crucial skill for any JavaScript developer. Fortunately, modern web browsers like Chrome, Firefox, and Edge come with built-in developer tools that make debugging easier. To access these tools, simply press F12 on your keyboard.

15. Explain the Symbols Used for Comments in Javascript.

This is one of the Java script interview questions that is usually asked. 

// for Single line comments and

/* Multi

Line

Comment

*/

16. What is Variable Typing in JavaScript?

In JavaScript, we can assign different types of values to variables. For example, you can store a number like 42 or a text string like "Hello, world!" in a variable.

17. What are Cookies?

Cookies are small text files that websites store on your computer. When you visit a website, the website can send a cookie to your computer. Moreover, this cookie contains information about your visit, such as your preferences, login information, or items in your shopping cart.

18. Explain Event Handlers in JavaScript.

The upcoming section will discuss one of the most important javascript questions and answers.  

Events are actions that happen on a webpage, such as clicking a button, hovering over a link, or submitting a form. To respond to these events, we use event handlers.

19. Explain ECMAScript.

ECMAScript is a programming language that forms the basis for JavaScript. In other words, it's a set of rules and standards that define how JavaScript works. As a result, it's widely used to create interactive web pages and applications.

20. What is NaN in JavaScript?

NaN stands for "Not a Number" in JavaScript. It's a special value that indicates an invalid numerical result. For example, when you try to divide a number by zero or perform a mathematical operation on a non-numeric value, JavaScript will return NaN.

Conclusion

JavaScript is a powerful language that's essential for building modern websites. It's used to create dynamic and interactive web pages. Therefore, understanding JavaScript's core concepts and best practices is crucial for web developers. This guide has covered many important JavaScript interview questions and answers, from basic concepts to more advanced techniques. However, remember that practice is the key to mastering JavaScript. So, keep exploring, experimenting, and building projects to improve your skills.

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