Top 24 JavaScript Interview Questions and Answers 2025

JavaScript, as most programmers already know, is an open-source scripting language. It is made for developing web-based apps. It is significantly quicker than other languages since it is easy to learn and interpretable. It is quite known that both HTML and JavaScript are interlinked. Given this, using JavaScript in web-based applications has become simpler than ever.

The Hero Vired team has put together a comprehensive list of the best Javascript Interview Questions and Answers to help you ace the job interview and earn your dream position as a Javascript Programmer. 

Introduction to JavaScript Interviews

Given its exceptional performance and next-level capabilities, most big corporations like Netflix and Google are now applying JavaScript in the majority of their operations. You must be competent and knowledgeable enough to clear your online assessment round and answer the JavaScript interview questions to secure a position as a web developer in one such corporation.

To help you prepare for all JavaScript questions, Hero Vired presents a guide to JavaScript interview questions and answers.

We bring to you the top JavaScript interviews questions with sample answers that would help demonstrate your knowledge of the industry and the job role.

1. Explain the basics of the JavaScript?

Brendan Eich, a Netscape programmer, created JavaScript. JavaScript was originally known as Mocha when it first debuted. Following that, it was referred to as Live Script until it became JavaScript. Web browsers that support object-oriented scripting may understand and carry out JavaScript code when it is put into HTML pages.

JavaScript has a number of features, including:

• Excellent option for network-centric applications
• Lightweight and simple to use
• Complementary to both Java and HTML
• Interpreted programming language
• Open-source cross-platform

2. What is JavaScript?

JavaScript needs no introduction as it’s a highly recognized scripting language in the programming world. It is distinct from Java language.

It is a lightweight, object-based, cross-platform translation language frequently utilized for client-side validation. The JavaScript Translator must interpret the JavaScript code for the web browser, which is built into the browser.

3. What are some advantages of JavaScript?

The benefits of JavaScript are as follows:

• Superior Interaction: JavaScript normally makes static web pages interactive and allows them to respond to user input.
• Quick Response: There won’t be any need to reload a web page when JavaScript is put into action.
• Excellent User Interface: The user interface (UI) of web apps can look and feel significantly better, thanks to JavaScript.
• Frameworks: Creating web-based applications and games becomes simpler with the vast frameworks and libraries available in JavaScript

Let’s move to the next javascript interview question.

4. What is Hoisting in JavaScript?

One of the most important JavaScript interview questions is  what hoisting is. The way that JavaScript operates by default is called hoisting, meaning that all variable and function declarations are shifted to the top. Hoisting, to put it simply, is the procedure of moving variables and functions up to the apex of the scope, regardless of where they’ve been declared. The reach can be local or international.

5. What are the different data types present in JavaScript?

Often, interviewers start with basic JavaScript interview questions, such as the data types available in JavaScript. Simply tell, JavaScript consists of two data types:

• Primitive data types and
• Non-primitive data types

6. What is the difference between the var and let keywords in JavaScript?

When it comes to JavaScript interview questions and answers, prepare this comparative analysis answer to what distinguishes var and let keywords. In JavaScript, both let and var keywords are leveraged to declare variables. Nevertheless, they have their differences, such as

Intermediate JavaScript Interview Questions and Answers

Here are some JavaScript interview questions and answers for intermediate level to prepare during your interviews.

7. What is the NaN property in JavaScript?

The NaN function in JavaScript is applied to check if a value is NaN (Not a number) or of the type “Number.” The expression NaN is a type of number in JavaScript. This is yet one of the JavaScript interview questions that you must stay aware of.

Let’s move to the next javascript interview question.

8. What is an Immediately Invoked Function in JavaScript?

Such javascript interview questions can be difficult but here’s a hint.

Immediately Invoked Functions, often known as IIFEs or IIFYs, begin operating as soon as they are specified.

Syntax:

(function()

{

// Do something;

})

();

9. What do you mean by strict mode in JavaScript, and what characteristics of JavaScript strict mode?

A brand-new tool in ECMAScript 5 called JavaScript Strict Mode enables you to create a function or code in a “strict” operational setting. This language typically throws errors that are “not especially severe.” Yet, in “Strict mode,” all errors, even silent faults, will result in a throw. Debugging hence becomes easier. This reduces the likelihood of programming errors.

10. What do you mean by Self Invoking Functions?

Self Invoking Functions are automatic function expressions that are invoked without a request when they are followed by (). However, the function declaration cannot be used by itself to call the function.

11. What is the difference between exec () and test () methods in JavaScript?

Knowing about the differences between exec() and test() will come in handy when preparing JavaScript interview questions and answers.

12. Explain Scope and Scope Chain in JavaScript.

The scope of a JS program controls which parts of the code allow access to variables and functions. In general, the scope will inform us of the variables and functions we can and cannot access at a particular location in the code. In JS, there are three different scope types:

• Function or local scope
• Global scope, and
• Block scope
• Scope Chain: The JavaScript engine leverages scope to locate variables as well.

13. What are some advantages of using External JavaScript?

External JavaScript is JavaScript code (script) that is created in a different file with the extension.js. This file is linked inside the head> or body> element of the HTML file, depending on where the code is to be inserted. Several benefits of external Javascript include.

It makes it possible for web developers and designers to work together on HTML and JavaScript files. The code is reusable. External JavaScript has simple code that is easy to read.

Let’s move to the next JavaScript interview question.

14. What is Currying in JavaScript?

Currying is also an important term asked in one of the JavaScript questions. Currying is the method of breaking down a function with many arguments into a series of functions, each containing just one argument. It is a mathematical technique that bears Haskell Curry’s name.

An n-ary function can become a unary function by performing currying. To illustrate how an n-ary function becomes a currying function, let’s look at an example.

Advanced JS Interview Questions and Answers

Here are some JavaScript interview questions and answers for advanced level preparation during your interviews.

15. What are the Types of Errors in JavaScript?

You may anticipate being asked one of the most common JavaScript interview questions: ‘what are the types of JS errors?’ Well, in JavaScript, there are two distinct forms of errors.

• Syntax error: Syntax errors are grammatical or spelling issues in the code that prevent the program from operating at all or from running fully. Typically, error messages are also provided.

• Logical error: Errors in reasoning happen whenever the syntax is correct, yet the logic or program is flawed. The output results, though, are false. These can occasionally be more challenging to fix than syntax errors because these applications don’t show error signals for logic errors.

16. What is the use of a constructor function in JavaScript?

Such Javascript interview questions can be difficult but here’s a hint.

The interviewer may test your knowledge of JavaScript’s constructor function, too, by asking one of the related JavaScript interview questions. Single or many objects with similar characteristics and methods can be created using constructor functions. Example:

17. What is DOM?

DOM or document object model represents the HTML document. It can be utilized to access and modify HTML information. Keeping your answer simple and concise for one such JavaScript question is good.

18. In JavaScript, what is an argument object?

JavaScript’s variables serve as a representation of the arguments supplied to functions.

19. What is the use of a window object?

The object that represents a browser window is produced automatically by the browser. There is no JavaScript object for it. That thing is a browser object. The popup dialogue box is shown using the window object.

Let’s move to the next JavaScript interview question.

20. How to write a comment in JavaScript?

In JavaScript, comments can be of two different types.

• A single-line comment The symbol for it is // (double forward slash).
• Multi-Line comment: Slash displays it as /* put a remark here */ with an asterisk.

21. What is the difference between JavaScript and JScript?

Conclusion

Hopefully, with these JS interview questions and answers, you now have the knowledge and a better grasp of the JavaScript questions that interviewer may ask in your coming interview. Being aware and knowing all these JavaScript interview questions and their responses is all good.

However, what should one do to acquire the skills to benefit from JavaScript’s popularity? No worries as Hero Vired has a solution for everything. With Hero Vired’s full-stack development course, you’ll never have to find answers to any JS interview questions whatsoever.