10 Most Common JavaScript Interview Questions for Front-End Developers

 

Introduction

Explain the importance of JavaScript in front-end development and its role in creating dynamic and interactive web applications. Highlight the purpose of the blog post, which is to prepare readers for common questions they might face in a JavaScript interview.

Common JavaScript Interview Questions and Answers

1. What is a closure in JavaScript, and how does it work?

   • Explanation: Discuss closures as a feature where an inner function has access to the outer (enclosing) function’s variables—scope chain.

2. Can you explain the difference between var, let, and const?

   • Explanation: Outline the differences in scope, hoisting, and reassignment properties of these declarations.

3. What are the different types of data types present in JavaScript?

   • Explanation: List and explain primitive types (such as undefined, null, boolean, string, number, bigint, symbol) and their behaviors.

4. How does prototypal inheritance work in JavaScript?

• Explanation: Describe the concept of objects inheriting properties and methods from other objects.

1. What is event delegation in JavaScript?

   • Explanation: Explain how event delegation is used to handle events efficiently at a higher level in the DOM than the original element that interacted.

2. What are promises and how do they work?

   • Explanation: Discuss the role of promises in handling asynchronous operations, their states (pending, fulfilled, rejected), and methods like .then(), .catch(), and .finally().

3. What are some of the ES6 features that have changed JavaScript development?

   • Explanation: Introduce features like arrow functions, template literals, destructuring, modules, etc.

4. How can you improve the performance of a JavaScript application?

   • Explanation: Talk about optimization techniques such as minifying scripts, lazy loading, and avoiding memory leaks.

5. Can you explain the difference between synchronous and asynchronous functions?

   • Explanation: Describe the execution differences, giving examples of synchronous/blocking operations versus asynchronous/non-blocking operations.

1. What are JavaScript Design Patterns that you are familiar with?

   • Explanation: Discuss commonly used design patterns like Module, Prototype, Observer, and Singleton.