Popular JavaScript Interview Questions and Answers 2024

Java is an OOPs programming language that must be compiled and JavaScript is an OOP scripting language completely in text.

JavaScript is a scripting language with the OOPs (object-oriented language) capability to create dynamic and interactive web pages like browsers and applications. At current, JavaScript is used as a server-side scripting language.

Developers can use JavaScript to create applications for mobile and desktop, front-end web development, and back-end web development, can write plugins for popular applications, and improve the future of artificial intelligence. 

Our meticulous sections of JavaScript interview questions and answers focus on beginners to the professional level of preparation. The curated lists of top JavaScript interview questions are frequently asked. 

To secure the position of a programming professional, a candidate needs to have in-depth knowledge of JavaScript interview questions. The tricky JavaScript interview questions lay in-depth knowledge on the subjects and help candidates crack insights and secure a good job in the market.

Lists of Top 20 JavaScript Interview Questions and Answers in 2024

The following JavaScript interview questions are divided into four sets for freshers to professionals to make interview preparation at its best.

It is highly beneficial to go set by set in your interview preparation and seize the best positions.

Basic JavaScript Interview Questions and Answers – Set 1

Below are the basic JavaScript interview questions with answers for freshers at a basic level,

1) What is hoisting in JavaScript?

Hoisting is the JavaScript default behavior of moving all the declarations of functions, variables, or classes to the top of the current scope before code execution.

2)Explain closures.

In programming languages, a closure (lexical closure or function closure) is a technique for storing a combination of functions together with references to a lexical environment. In JavaScript, closures get implemented during the creation of a function.

Suggested Read: Java Interview Questions And Answers 2024 (UPDATED)

3) What is a “debugger” statement in JavaScript?

The debugger statement stops the execution of the code at a breakpoint in JavaScript and calls the debugging function.

Also, the debugging statement fails to work without the availability of debugging functionality.

4) What are first-order functions?

A programming language is said to have first-class functions treated as the first-class object that supports all the operations allowed to objects in JavaScript.

5) What are higher-order functions?

A higher-order function in JavaScript is a function that accepts a function as an argument or returns a function. 

6) Why use the typeof operator?

The typeof operator in JavaScript checks the type of variable.

Advanced JavaScript Interview Questions and Answers – Set 2

Let’s look at a few of the answers to the advanced JavaScript interview questions,

7) What is DOM?

DOM (Document Object Model) is a programming interface for web documents. It is used to manipulate HTML files (the content, structure, and style of a document).

8) Name the different methods to create JavaScript objects.

Several methods in used to create or declare an object in JavaScript;

- Object Literals.

- Keyword New.

- Object Constructor.

- Object.create().

- using Function.

9) Explain WeakMap in JavaScript.

A weak map is a compilation of key-value pairs where the keys are poorly referred to. These keys must be objects with values of any arbitrary JavaScript type with weak references to its keys.

10) What is the main difference between ‘==’ and ‘===’?

They are both comparison operators. The only difference is that the ‘==’ compares if the two given values are equivalent, whereas, the '===' operator checks the given values and types.

11) Define debouncing.

Debouncing is a JavaScript technique to accelerate browser performance. The method is in frequent use for low-loading computations and features of a webpage with low performance. The debounce function for the code is only triggered once per user input.

Experienced JavaScript Interview Questions and Answers – Set 3

Given below are the JavaScript interview questions for experienced along with the best answers,

12) How to add JavaScript to an HTML file?

To use a script tag to add a JavaScript file in an HTML file. 

For instance;

13) Mention the three types of JavaScript errors.

There are three main types of errors in JavaScript programs namely; syntax errors, runtime errors, and logical errors.

Syntax Error: A fault in the syntax of the program that is incorrect.

Runtime Error: A software or hardware error that takes place during program runtime after it's interpreted by the compiler.

Logical Error: A difficult error to identify where the syntax is correct but the logic is wrong.

14) What are async and defer?

Both the async and defer load JavaScript asynchronously in absence of render-blocking.

Async executes the script as soon as possible while parsing the HTML. Whereas, defer runs in sequence and executes the script only after parsing the HTML

15) Is JavaScript language dynamic or static?

JavaScript is a dynamic language.

Technical JavaScript Interview Questions and Answers – Set 4

Here are the JavaScript technical interview questions along with the best answers for experienced professionals or freshers,

16) What is the difference between null and undefined in JavaScript?

The major differences include;

Null: The value of the variable is intentionally absent.

Undefined: The value of the variable does not exist in the compiler or program.

17) Define Prototype Chaining.

When the prototype of an object accesses the same property from the constructor function, the object inclines to extract the property from the constructor function.

This type of linking to another is called Prototype chaining or Prototype chain in JavaScript.

18) Define BOM.

BOM (Browser Object Model) is the core of Javascript on the web that helps to interact with the browser.

It means that objects are exposed by the web browser for modifying properties and objects referenced to them.

19) What is the use of isNaN?

In JavaScript, isNaN (is Not a Number) or sNaN() is used to check whether a given value is a number or not. If the value is a number then it returns false else it returns true.

20) What is the use of “Use Strict”?

The main purpose of “use strict” is to indicate that the code should be executed in “strict mode”.

Takeaway

From search engines to Meta platforms, JavaScript is used widely to create complex and desktop-like applications.

It is necessary to tackle the JavaScript top interview questions fully prepared as the probability of such interview questions on JavaScript is expected. In general, these are the mostly asked questions in JavaScript.

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Frequently Asked Questions

1) Should I use strict JavaScript?

It can be used during optimizations to eliminate silent errors in the code.

2) Where to practice JavaScript interview questions?

Below are some of the best platforms to practice JavaScript,

- Codedamn

- Codewars

- CodinGame.

- Edabit

- HackerEarth

- Solo Learn

- Programiz

- Freecodecamp

3) Can I learn JavaScript in 2 days?

With a consistent study plan, the learners can expect to take six to nine months to achieve a working proficiency in JavaScript.

4) How can I effectively communicate my problem-solving approach during a JavaScript interview?

Break down problems into smaller steps, articulate your thought process clearly, and seek feedback. Communication is key, so explain your code, discuss trade-offs, and be open to collaboration during the interview.

5) How can I stand out in a JavaScript technical interview?

Go beyond basic answers. Discuss real-world applications of JavaScript in your previous projects. Demonstrate knowledge of tools like Webpack, Babel, or testing libraries. Show enthusiasm for staying updated on the latest trends and frameworks