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Top 12 JavaScript Interview Questions

Posted in Programming   OCTOBER 11, 2021

Javascript Interview question

The market and technological stack for the information technology sector have evolved considerably throughout the years. The number of frameworks, libraries, tools, and languages available for developing technological applications continues to grow and improve significantly. Javascript is one such language that has risen to prominence as one of the most popular in the information technology sector.

If you're interested in technology, Javascript is not just a popular and useful language; it also provides a potential career and pays opportunity.

As anticipated, the employment market for Javascript developers is competitive; although it's simple to pick up the fundamentals, landing your first job as a Javascript developer is not easy. However, do not be alarmed; we are not frightening you. There is a method to ace your interview for Javascript programming.

We've prepared a list of the top 12 Javascript interview questions in today's article to assist you to get a job as a Javascript developer at your ideal business. The blog is a collection of frequently asked questions from Javascript developers. We've attempted to cover some critical points for each domain in which Javascript is utilized. We also have a Full certification Interactive course on Javascript. We hope you take advantage of these opportunities!

Part I - Interview Questions for JS (Basic)

This first section discusses fundamental JS Interview Questions and Answers.

Q1. What is JavaScript?

JavaScript is a programming language that is mainly used to create web pages and to provide functionality to online applications.

Q2. What is JavaScript and how does it work?

This is a list of frequently requested JS Interview Questions. Each browser relies on three critical components to function properly. The first is an interpreter for the DOM (Document Object Model). This will take your HTML page and transform it into a format that can be seen in a browser. The second tiny application included with the browser is a CSS interpreter, which will style and improve the appearance of the page. The last one is a browser-based mini-program called the JS engine.

  • The HTML/JS file is loaded by the browser.
  • JavaScript is a scripting language that is interpreted (means no compilation required)
  • The browser (JavaScript engine) runs each line in turn and waits for events (such as clicks, mouseovers, and so on) to occur.

Q3. What are some of JavaScript's features?

The following sections discuss the various aspects of JavaScript:

  • JS is a concise, interpreted programming language.
  • JS is an open-source, cross-platform programming language.
  • JS is a component of HTML and Java.
  • Designed to facilitate the development of network-centric applications

Q4. In terms of JavaScript, what are the various kinds of data?

  • Strings
  • Functions
  • Boolean
  • Object
  • Number
  • Undefined

Q5. What are the most often occurring mistakes in JavaScript?

In general, there are three kinds of errors that we encounter in JS.

  • Runtime error: This is the result of the HTML language's instructions being abused.
  • Load time error: This is a syntax error that is dynamically produced.
  • Logical error: This error happens when the logic of the functions is incorrectly executed.

Q6. Justify your choice of JS as a Case-Sensitive Language.

JS is a case-sensitive computer programming language. In JS, we utilize a variety of different kinds of variables, functions, and other identifiers that should all be consistent.

JS Interview Questions - Part 2 (Advanced)

Q7. What are some of the benefits and drawbacks of JavaScript?


  • A well-designed user interface
  • Increased interactivity(when a mouse hovers on elements like buttons or keyboard accessibility)


  • It is deficient in multithreading activities.
  • Incompatibility with networking applications
  • Client-side JavaScript is not a readable or writable language.

Q8. What are the different types of objects in JS and how are they defined?

In JS, there are two kinds of objects:

  • Date Object: This is created using the JS programming language. These are generated using a new date and may be handled using a variety of ways after they are created. This contains the date object's year, month, day, hour, minute, second, and even milliseconds. These are established using local norms of universal time.
  • Number Object: Dates are included in this category since they are exclusively represented by integers and fractions. The literals of the numbers are immediately transformed to the number class

Q9. What does the term "closure" mean in JavaScript?

When we create a function inside another function (also known as a parent function) and access the variables specified in the parent function. The closure has three contexts in which it may access variables:

  • Declared variables with their own scope
  • Variables defined inside the scope of a parent function
  • Variables declared global namespace variables



the inner function is a closure defined within the outer function that has access to all variables declared and defined within the outer function's scope. Additionally, the function specified as a closure inside another function has access to variables declared in the global namespace.



Q10. In JavaScript, how can I empty an array?

This is a common JS Interview Question that is asked during an interview. By using any of the mentioned techniques –

  • arrayList = [ ]

The above code creates a new empty array in the variable ArrayList.

  • length =0;

To begin, the above code zeroes the length of the existing array. This method is helpful when you wish to update all other variables that relate to ArrayList.

  • splice(0, ArrayList.length);

This method of emptying the array will also update all of the array's references.



This is one method of emptying the array.

Q11 Describe a few JavaScript datatypes.

In general, these data types include the value. There are two distinct data kinds in JS.

  • Primitive datatypes
  • Non-primitive datatypes
  • String, Number, Boolean, Undefined, and Null are considered primitive data types, while Object, Array, and RegExp are considered non-primitive data types.

Q12. What do you mean by JavaScript functions?

Functions are a collection of reusable code. This enables a user to create a specific piece of code and call it as many times as necessary. It is not required to use a JS function to return a value. There are two distinct kinds of functions JS supports-

  • Anonymous functions
  • Named functions

JS function syntax –

Function functionName(parameter1, parameter2,......parameter n)

{//statement of the fucntions


To define a function, we must use the function followed by the name of the function and parentheses. We must provide the function arguments inside the parentheses (can have multiple parameters).

To call the function, we just provide its name and the argument values inside parentheses (pass the values).

addNumbers(x1, x2) — in this case, we've specified the values and invoked the function.

Getting ready for your interview

As is the case with any other talent, the only way to improve is to practice. Interviews for technical positions are no different. While you cannot anticipate every potential question, every extra minute spent practicing before an interview increases your chances of success.

Explain your responses and how you got at them in detail throughout the interview. This enables the interviewer to get a better understanding of your thought process. Whether you answer a question incorrectly, the interviewer may examine your method to see if you were on the right road.

With enough preparation, you should have no difficulty passing your next technical interview!