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Top 30 JavaScript Interview Questions You Must Know

Svetloslav Novoselski 34

Top 30 JavaScript Interview Questions You Must Know

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Top JavaScript Interview Questions
Top JavaScript Interview Questions

In this article you can find some of the top JavaScript interview questions, If you find yourself on the job hunt or getting ready for an upcoming interview, this article is for you. Enjoy reading!

Question 1: What is JavaScript, and what are its key features?

Answer: JavaScript is a versatile, high-level programming language used for web development. Its key features include:
- Interactivity: JavaScript allows you to create interactive elements on web pages.
- Client-Side Scripting: It runs on the user’s browser, enabling dynamic content.
- Event Handling: JavaScript handles user interactions like clicks and form submissions.
- Asynchronous Programming: It supports asynchronous operations with callbacks and promises.

Question 2: Explain the difference between null and undefined.

Answer: null represents an intentional absence of any object value, while undefined indicates a variable has been declared but not assigned any value.

let a; // undefined
let b = null; // null

Question 3: What is a closure, and why is it important?

Answer: A closure is a JavaScript function defined within another function, allowing it to access its outer function’s variables. Closures are crucial for encapsulation and data privacy.

function outer() {
let message = “Hello, “;

function inner(name) {
console.log(message + name);
}

return inner;
}

const greeting = outer();
greeting(“Alice”); // Outputs: “Hello, Alice”

Question 4: Explain the event delegation concept.

Answer: Event delegation is a technique where a single event handler is attached to a common ancestor for multiple child elements. It improves performance and reduces memory usage by avoiding the need to attach individual handlers to each element.

<ul id=”list”>
<li>Item 1</li>
<li>Item 2</li>
<li>Item 3</li>
</ul>

<script>
document.getElementById(‘list’).addEventListener(‘click’…