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Top 20 JavaScript Interview Questions and Answers

Published On: June 10, 2024

JavaScript Interview Questions and Answers

JavaScript is a programming language, and it is used to develop web servers, games, mobile and online apps, and more. The SLA experts curated a list of the top 20 JavaScript interview questions and answers to help you ace the interview and land your dream position as a JavaScript developer. 

JavaScript Interview Questions and Answers for Freshers

1. What is JavaScript?

JavaScript is a well-liked web scripting language that is useful for both client-side and server-side programming. Web browsers that parse and run HTML pages can have JavaScript added to them. JavaScript is compatible with object-oriented programming.

2. What features does JavaScript have?

JavaScript has the following features:

  • Programming language that is lightweight and interpretable, suitable for multiple systems
  • Object-oriented code source
  • combining a variety of back-end and front-end technologies
  • specifically utilized in the creation of network-based applications

3. What does JavaScript’s “this” keyword mean?

The JavaScript keyword “this” identifies the object now being called. Constructors typically use it to set the values for object properties. 

4. What are the scopes of a variable?

In a JavaScript application, a variable’s scope refers to the location of its declarations and definitions. A variable can have one of two scopes:

Global Scope: Variables with global scope can be accessed from anywhere in JavaScript code.

Local Scope: Only the function that has a local variable can access it. 

5. What are the JavaScript naming conventions for variables?

The following are the guidelines for naming variables in JavaScript.

  • Variable and reserved keywords cannot share the same name. Examples include var, let, and const.
  • Variable names cannot start with a number. At first, they can only contain letters or underscores.
  • It matters when it comes to variable names.  

6. How is JavaScript code debugged?

Any modern web browser, such as Chrome, Firefox, and others, includes an integrated debugger that can be accessed at any time by pressing the appropriate key, which is usually F12. Debugging tools enable users to perform a wide range of operations.

Furthermore, we can debug JavaScript code straight from within a code editor used to create JavaScript apps, such as Visual Studio Code, Atom, Sublime Text, or another one.

7. What does JavaScript callback mean?

JavaScript functions can accept input from other functions and return objects from other functions since they are objects.

Callbacks are JavaScript functions that are provided as arguments or parameters to other functions. This function will be called whenever the provided function is run. 

8. Tell me how you will add JavaScript code to an HTML file.

There are two major ways to embed JavaScript code:

  • When only a few lines of scripting are required on a web page, we can write JavaScript code within the script element of the same HTML document.
  • When a JavaScript source file is imported into an HTML document, the entire web page can be created without clogging the code.  

9. Explain cookies.

A cookie is often a short data file transmitted and saved on the user’s computer by the web browser used to access the website. Cookies are used to store data for later use and to monitor user behavior on websites.

10. Differentiate between Var and Let.

In JavaScript, utilize the let and var statements to specify variables and methods. A block scopes the let keyword, while a function scopes the var keyword. Aside from that, not much distinguishes the two.

11. How to create a cookie using JavaScript?

The most simple approach for creating JavaScript cookies is as follows:

document.cookie = “key1 = value1; key2 = value2; expires = date”;

12. What JavaScript arrow functions are there?

Arrow functions allow you to write JavaScript functions quickly and simply. 


const helloWorld = () => {

console.log(“hello world!”);


13. Why is the isNaN function used?

The number isNan function determines whether the provided value is of the type “Number” or NaN, which means “Not a number.” The value NaN is regarded as a type of number in JavaScript. The function returns true if the argument is not a number, and false if it is.

14. Which is quicker between ASP and JavaScript?

JavaScript executes faster than ASP Script. JavaScript is a client-side programming language, which means it operates independently of the server. ASP is a server-side scripting language that remains persistently stable on the server.

15. Explain negative infinity

The lowest value that can exist is represented by the constant value of negative infinity. It means that this value cannot be lowered by any other number. It can be generated by an arithmetic procedure or a self-made function. In JavaScript, the value of NEGATIVE_INFINITY is shown as -Infinity.

JavaScript Interview Questions and Answers for Experienced

16. Can JavaScript code be divided into multiple lines?

It is possible to split the JavaScript code into many lines within a string statement. To break it, use the backslash ‘\’.


document.write(“A Lifetime Career Guidance\ by SLA”)

The code-breaking line is avoided by JavaScript, which is not optimal.

let gfg= 10, GFG = 5,


gfg + GFG;

17. Describe JavaScript’s Higher Order Functions.

Higher-order functions are those that perform operations on other functions, either by returning them or by accepting them as arguments.

Because functions in JavaScript are first-class citizens, they lead to higher-order functions.


function higherOrder(fn) {



higherOrder(function() { console.log(“Hello world”) });  

function higherOrder2() {

  return function() {

    return “Do something”;



var x = higherOrder2();

x()   // Returns “Do something”

18. What is a self-invoking function in JavaScript?

A self-invoking expression is automatically invoked (initiated) without any request. A function expression will run automatically if it has an a() after it. It is not possible to call a function definition by itself.

An anonymous function can be used to run a function automatically when it is described; otherwise, it will not be called again. Normally, we define functions and call them. Furthermore, these kinds of functions have no name.

19. What distinguishes JavaScript’s exec() and test() methods from one another?

  • JavaScript uses the RegExp expression functions test() and exec().
  • To search a string for a specific pattern, we’ll use exec (). If the pattern is found, the function will return it straight; if not, it will return ’empty’.
  • To locate a string for a given pattern, we’ll utilize test(). When it locates the provided text, it will return the Boolean value “true”; otherwise, it will return “false.”

20. What benefits does utilizing External JavaScript offer?

External JavaScript refers to JavaScript code (script) that is written in a different file ending in.js. It is linked inside the element of the HTML page that contains the code.

A few benefits of using external JavaScript are

  • It allows designers and web developers to collaborate on HTML and JavaScript files.
  • The code can be used again.
  • The readability of code in external Javascript is straightforward.


We’ve included some of the most often-asked JavaScript interview questions and answers in this list to help you navigate the interview process. Join our JavaScript training in Chennai to kickstart your web development career.

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