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Javascript Interview Questions and Answers

JavaScript, created by Brendan Eich in 1995, is one of the most widely used web development languages. It was designed to build dynamic web pages at first. A script is a JS program that may be added to the HTML of any web page. When the website loads, these scripts begin to run automatically. 

JavaScript is being used by Google, Instagram, and Facebook, among others, to create powerful, desktop-like web apps. Node.js has been one of the most popular languages for developing server-side software since its release. Even today, the web isn’t large enough to accommodate JavaScript’s variety. So, if you’re considering a career in JavaScript and want to learn the skills required, now is the time to get in while the technology is still in its infancy. JavaScript Coding Interview Questions will provide you with a thorough understanding of the language and assist you in preparing for your interviews.

JavaScript Coding Questions for beginners

1. Where does Javascript belong to?

Oracle Corporation owns the trademark “JavaScript” in the United States.

2. How much percentage of websites use JavaScript for client-side scripting? 

For client-side scripting, almost 80% of websites employ a third-party JavaScript library or web framework.

3. What index language is JavaScript?

Zero-index language. 

4. What is JavaScript, and how does it work?

This is one of the basic JavaScript Coding Interview questions; JavaScript is an object-oriented, trivial interpreted programming language that allows you to add interactivity to otherwise static HTML websites. The language’s all-purpose fundamental has been integrated into Netscape, Internet Explorer, and other web browsers.

5. What are the benefits of using JavaScript?

These are some of the benefits of using JavaScript: 

Less server interaction User input can be validated before the page is sent to the server. This reduces server traffic, resulting in lower stress on your server.

Visitors get immediate feedback; they don’t have to wait for the page to reload to discover if they’ve forgotten something.

Increased interactivity: You may make interfaces that respond when the user moves their mouse over them or activates them with the keyboard.

Wealthier interfaces Using JavaScript, you may add drag-and-drop components and sliders to create a rich interface.

6. There is a distinction between the operators ” == ” and ” === “. What is it?

Both of these operators are comparison operators. The distinction between the two operators is that “==” compares values, whereas “=== “compares both values and types.

7. Is JavaScript a statically or dynamically typed programming language?

For this JavaScript coding interview question, you can answer; A dynamically typed language is JavaScript. The type of a variable is checked during run-time in a dynamically typed language, whereas the type of a variable is checked during compile-time in a statically typed language.

8. In JavaScript, what are the scopes of variables?

A variable’s scope is the area of your program where it is specified. Only two scopes will be available for JavaScript variables.

Global Variables have a worldwide scope, which means they are perceptible throughout your JavaScript code.

Local Variables A local variable is only visible within the scope of the function in which it is defined. Therefore, the parameters of a function are always unique to that function.

9. In JavaScript, what is the NaN property?

The “Not-a-Number” value is represented by the NaN attribute. It denotes a value that isn’t a valid number.

10. Explain the differences between passed by value and passed by reference.

This JavaScript coding interview question can be a little confusing. So be careful while answering it; Non-primitive data types are passed by reference in JavaScript, while primitive data types are supplied by value.

11. What is a JavaScript Immediately Invoked Function?

An Immediately Invoked Function (also known as IIFE or IIFY) is a function that starts running as soon as it is defined.

12. Explain the term “this.”

The keyword “this” refers to the object of which the function is a property.

The value of the keyword “this” is always determined by the object calling the function.

13. What is the best way to erase a cookie using JavaScript?

This JavaScript coding interview question can be answered by saying; Set the expiration date to a point in the past if you want to remove a cookie so that further attempts to read the cookie in JavaScript return nothing. To guarantee that you delete the correct cookie, you need to define the cookie path. If you don’t give the path, some browsers won’t let you erase a cookie.

14. How can I use JavaScript to read a cookie?

Because the cookie is the value of the document.cookie object, reading a cookie is just as simple as writing one. As a result, you can use this string to access the cookie at any time.

A list of term = value pairs disconnected by semicolons will be kept in the document.cookie string, where name is the name of a cookie and value is its string value. 

The split () function can be used to separate a string into keys and values.

Intermediate level JavaScript Coding Interview Questions 

1. How many different ways may JavaScript code be used in an HTML file?

This JavaScript coding interview question is an important one; 

A JavaScript code can be included in an HTML file in three different ways:

  • Inline
  • Internal
  • External

2. What’s the difference between properties and attributes?

Attributes—such as id, type, and value—provide additional information about an element.

The value assigned to the property, such as type=”text”, value=’Name’, and so on.

3. What is the distinction between innerHTML and innerText? 

  • innerHTML – If an HTML tag is detected in a string, it will be processed.
  • innerText — If an HTML tag is detected in a string, it will not be processed.

4. What are the differences between exports and imports?

Imports and exports make writing modular JavaScript code easier. We can separate our code into numerous files using imports and exports.

5. What is the definition of a typed language?

This is a crucial JavaScript coding question; Values are related with values rather than variables in typed languages.

6. What are the two types of it?

There are two types:

  • Dynamically
  • Statically

7. What is local storage, and how does it work?

For each HTTP request (HTML, pictures, JavaScript, CSS, and so on), the data is not sent back to the server, decreasing the amount of traffic between the client and the server. It will remain until cleared manually through settings or an application.

8. What is session storage and how does it work?

It works similarly to local storage, with the exception that data kept in session storage expires when the page session ends, whereas data stored in local storage does not. When the browser is closed, Session Storage is removed.

9. What are JavaScript frameworks, and how do you use them?

This JavaScript coding interview Question can be answered by saying;  A JavaScript framework is a JavaScript-based application framework. Its control flow differs from that of a JavaScript library.

10. Give examples of JavaScript Frameworks.

11. What’s the difference between undefined and null?

This JavaScript coding question can be answered by saying; The term “undefined” refers to a variable that has been declared but not yet given a value. Null, on the other hand, is a value assigned to a variable. It can be assigned to a variable as a no-value symbol. Undefined and null are also two different types: undefined is a type, whereas null is an object.

12. In JavaScript, how do you convert a string of any base to an integer?

To translate numbers between different bases, use the parseInt() method. The first parameter is the string to be translated, and the second parameter is the base of the given string.

13. What exactly is the distinction between undeclared and undefined?

Variables that do not exist in a programme and are not declared are known as undeclared variables. A runtime error occurs if the programme tries to understand the power of an undeclared variable. Undefined variables are variables that have been declared in the programme but have yet to be assigned a value.

JavaScript Coding Questions for advanced-level professionals 

1. In JavaScript, what is a prompt box?

This is a frequently asked JavaScript coding question;  A prompt box is a box that provides a text box for the user to enter input. The prompt () method displays a dialogue box that asks for input from the visitor. If you want the user to enter a value before proceeding to the next page, a prompt box is frequently used. After providing an input, the user must choose between clicking “OK” or “Cancel” in order to proceed.

2. In javascript, what is the purpose of promises?

In javascript, promises are used to handle asynchronous operations.

Callbacks were used to handle asynchronous actions before promises. However, because callbacks have limited capability, utilising many callbacks to handle asynchronous code might result in unmanageable code.

3. In JavaScript, what are escape characters?

This JavaScript coding question falls under the advanced category; JavaScript escape characters allow you to write special characters in your application without breaking it. When working with special characters such as single quotes, double quotes, apostrophes, and ampersands, escape characters (Backslash) are used. To make the characters appear, add a backslash before them.

4. What are the different types of arrow functions?

In the ES6 version of JavaScript, arrow functions were added. They give us a new, more concise syntax for declaring functions. Arrow functions can only be used to express a function.

5. In JavaScript, what are classes?

Classes are nothing more than syntactic sugars for functions, and they were introduced in the ES6 version. In JavaScript, they give a new manner of declaring functions. Classes, unlike functions, are not hoisted. Before a class is declared, it cannot be used.

6. What is Object Destructuring, and how does it work?

Object destructuring is a novel method of extracting elements from an object or array.

7. What is the definition of a Temporal Dead Zone?

Variables declared with the let and const keywords exhibit Temporal Dead Zone behavior.

8. What is JavaScript’s ‘Strict’ mode, and how do I enable it?

This is one of the most important JavaScript coding questions asked in an interview; Strict mode is a means to improve your code’s error-checking capabilities. You can’t utilise implicitly declared variables in strict mode, or assign a value to a read-only property, or add a property to a non-extensible object. You can enable strict mode by including the phrase “use strict” at the start of a file, a programme, or a command.


Preparing these JavaScript Coding Interview Questions will give you a strong theoretical base, and help you ace the interview. Remember to practice your coding material, read this article and memorise it thoroughly to perform well in your next interview. No matter which level you are in terms of knowledge of this topic, this article can be of great value.

More Resources : Freelance Digital marketing jobs | Freelance recruiter jobs | Business Development Executive Interview Questions | Logical Reasoning Questions and Answers

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