120 Advanced JavaScript Interview Questions

Introduction

Are you ready to elevate your JavaScript skills? Advanced JavaScript Interview Questions is your go-to guide for mastering JavaScript, whether you're a beginner or an expert.

In the dynamic world of web development, JavaScript reigns supreme. This book covers the entire spectrum, catering to entry-level coders, junior developers seeking growth, mid-level engineers aiming for proficiency, and senior developers pursuing excellence. Even seasoned experts will discover valuable insights to enhance their JavaScript proficiency.

01. Explain equality

Problem: JavaScript has both strict and type–converting comparisons:

Strict comparison (e.g., ===) checks for value equality without allowing coercion.

Abstract comparison (e.g., ==) checks for value equality with coercion allowed.

Solution:

const a = 42;

const b = 42;

console.log(a == b); // true

console.log(a === b); // false

Some simple equality rules: If either value (also known as side) in a comparison could be the true or false value, avoid == and use ===.

If either value in a comparison could be of these specific values (0, , or [] — empty array), avoid == and use ===.

In all other cases, you’re safe to use ==. Not only is it safe, but in many cases, it simplifies your code in a way that improves readability.

02. Understanding Exponential Operator

Problem: Explain the usage of the exponential (**) operator in JavaScript, including when and how to use it to perform exponentiation calculations.

Solution: The exponential operator (**) in JavaScript is used to perform exponentiation, which is raising a number to a power. It's a concise and intuitive way to perform such calculations.

Here's how to use it:

// Using the exponential operator

const result1 = 2 ** 3; // raised to the power of 3 console.log(result1); // 8

const result2 = 4 ** 8.5; // Square root of 4 console.log(result2); // 131072

const result3 = 10 ** -2; // 10 raised to the power of -2 console.log(result3) // 0.01

The exponential operator can be used with both integer and floating-point exponents. It's particularly useful when you need to perform exponentiation calculations in a clear and concise manner.

03. Change the title of the page

Problem: Changing Page Title

Solution: Using document.title Property

You can change the title of a webpage using the document.title property in JavaScript.

document.title = My New Title;

This is a straightforward task in JavaScript. Changing the page title is as simple as assigning a new value to the document.title property. It's a basic operation that most web developers should be familiar with, making it an easy problem. However, it's still an important concept to understand when working on web development projects.

04. Understanding JSON

Problem: Explain what JSON (JavaScript Object Notation) is and its purpose in web development.

Solution: JSON, short for JavaScript Object Notation, is a lightweight data interchange format that is easy for humans to read and write, and easy for machines to parse and generate. It is often used for exchanging data between a server and a web application, as well as between different parts of an application.

JSON is represented as key-value pairs, where keys are strings and values can be strings, numbers, Booleans, arrays, or other JSON objects.

The basic syntax of a JSON object looks like this:

{

key1: value1,

key2: 123,

key3: true,

key4: [item1, item2],

key5: {

nestedKey: nestedValue

}

}

JSON is widely used because of its simplicity, ease of use, and compatibility with various programming languages. It is a common format for sending and receiving data in web APIs, configuring applications, and storing configuration settings.

05. Discussing Data Types

Problem: Discuss the various data types available in JavaScript and provide examples of each.

Solution: JavaScript offers a range of data types for storing values:

These JavaScript data types enable value storage and manipulation in various ways, forming the foundation for dynamic and versatile programming.

06. Mixins and Achieving Multiple Inheritance

Problem: In JavaScript, there's no built-in multiple inheritance support, making it challenging to share functionalities across different objects efficiently. Traditional class hierarchies can become complex and rigid, hindering code maintainability.

Solution: Mixins offer a solution by enabling code reuse and achieving a form of multiple inheritance. A mixin is a way to incorporate methods and properties from one object into another. This enhances modularity and flexibility in code design.

Implementation: To implement mixins, you can use the Object.assign() method to copy methods and properties from a source object to a target object.

Here's a brief example:

const greetingsMixin = {

sayHello() {

console.log(Hello from mixin);

}

};

const objectA = {};

Object.assign(objectA, greetingsMixin);

objectA.sayHello(); // Hello from mixin

const objectB = {};

Object.assign(objectB, greetingsMixin);

objectB.sayHello(); // Hello from mixin

By applying mixins, you can achieve code reusability and avoid deep class hierarchies. However, be cautious of potential method conflicts and unintended overwrites when using multiple mixins.

07. How to Implement Polymorphism

Problem: Polymorphism is a fundamental concept in Object-Oriented Programming that enables objects to take on multiple forms. In JavaScript, polymorphism can be achieved using function overloading, where a function can have multiple implementations based on the number and type of arguments it receives.

Here's a simple example illustrating how function overloading can be implemented in JavaScript:

function greet(name, language = 'English') { if (language === 'English') {

console.log(`Hello ${name}`);

} else if (language === 'Spanish') { console.log(`Hola ${name}`);

}

}

greet('John'); // Hello John greet('Juan', 'Spanish'); // Hello Juan

Solution: In this example, the greet function accepts two arguments: name and language. The default value for language is set to English. If you call the function with only one argument, it will utilize the default language. However, when you call the function with two arguments, it will use the specified language.

This mechanism demonstrates how polymorphism can be achieved in JavaScript through function overloading, allowing a single function to exhibit different behaviors based on the input provided.

08. Understanding Arrays in JavaScript and their creation

Problem: Explain arrays in JavaScript, along with the process of