Object Oriented Programming (OOP) in JavaScript Complete Guide (2023)

Object Oriented Programming (OOP) in JavaScript Complete Guide (2023)


Definition of OOP

The “object-oriented programming” (OOP) paradigm is based on the premise that “objects” can contain both data and code that manipulates that data. In OOP, objects are instances of classes, templates, or blueprints used to create objects.

Comparison of OOP to other programming paradigms

Here are a few examples of comparisons between OOP and other programming paradigms:

Functional programming

OOP and functional programming are different in terms of their philosophy and approach to problem-solving. OOP focuses on the objects and their interactions, while functional programming focuses on the functions and the data they operate on.

Procedural programming

OOP can be seen as an extension of procedural programming, as it builds on the concepts of procedures and data structures. However, OOP adds the concepts of classes and objects, which provide a way to organize code and data into cohesive units. 

Logic programming

Logic programming is a paradigm based on the formal logic used to represent the knowledge of the domain and solve problems. OOP is a paradigm that is based on real-world object representation, and it is used to design software systems.

Benefits of using OOP in JavaScript

Object-oriented programming (OOP) can bring many benefits when used in JavaScript, some of them include:

Code organization

OOP is a way to organize code into reusable, self-contained objects that can be used over and over again. This makes it easier to understand and care for large, complicated systems.


OOP allows you to hide the internal state and behavior of objects, which can provide a way to protect data and methods from unauthorized access and also make the code more robust.


OOP allows you to inherit properties and methods from parent objects, which can be valuable for code reuse and complexity reduction.


Object-oriented programming allows objects to take on various forms, making code more adaptive to changing requirements.


OOP allows you to abstract away from the implementation details of an object and focus on its behavior, making the code more readable and maintainable.


OOP allows you to divide the code into small, independent, and reusable units (objects), making it easier to understand and maintain.

Classes and Objects

Definition of classes and objects

A class serves as an object’s blueprint and specifies the attributes and operations that belong to that class. It defines the structure of the object, but it does not create any actual object. A class can be considered the blueprint of an object, consisting of a set of properties and methods.

An object has its own properties and methods and is an instance of a class. Objects are created by using the new keyword followed by the class name. Objects are the instances of a class, and they can be created by using the class name with the new keyword. Each object has its properties and methods defined in the class.

Creating classes and objects in JavaScript

In JavaScript, classes and objects can be created using the class keyword introduced in ECMAScript 6.

A sample of how to construct a class called “Human” is provided below:

class Human {     constructor(myName, year) {       this.year = year;       this.myName = myName;     }     speak() {       console.log(`Hi, my name is ${this.name} and I was born in ${this.age}!`);     }   }
Code language: JavaScript (javascript)

This class has a constructor function that is used to set the initial properties of the object, in this case, the name and age. The class also has a method called speak() that can print a message to the console.

The new keyword can be used to instantiate an instance of this class:

let human1 = new Human("Stewie", 2003); human1.speak();
Code language: JavaScript (javascript)

Constructors and methods

Object-oriented programming (OOP) uses a constructor to initialize an object when it is first created. It is responsible for setting the object’s initial state and allocating any necessary resources. A constructor is typically defined using the ‘constructor’  keyword within a class.

On the other hand, a method is a function connected to an object or class that may be utilized to carry out operations on the object or class. Methods are defined within the class or object and can be called on instances of the class or object. Methods are usually used to implement how an object or class works.

Inheritance and polymorphism

Inheritance and polymorphism are two essential concepts in object-oriented programming (OOP) that can be used to improve code reuse and flexibility.

It is a mechanism that allows objects to inherit properties and methods from parent objects. This allows for code reuse, as common properties and methods can be defined in a parent object and then inherited by child objects.

JavaScript uses a prototype-based inheritance, where objects inherit properties and methods from their prototypes. This can be achieved using the prototype property of a class or constructor function.

The ability to handle objects from various classes as though they were members of the same class is known as polymorphism. This allows for code that can work with multiple types of objects, and it is achieved through interfaces and virtual functions in some languages.

JavaScript does not have explicit support for interfaces or virtual functions. Still, it can achieve polymorphism through function overloading and by using the prototype chain, as well as the instance of the operator.

Encapsulation and Access Modifiers

Definition of encapsulation

In object-oriented programming (OOP), encapsulation combines data and the functions that work with that data into a single entity (an object).

This bundling is done to hide the implementation details of an object from the outside world and to protect the data from unauthorized access.

Implementing encapsulation in JavaScript

In JavaScript, encapsulation can be achieved through closures and this keyword and by using the let and const keywords to limit the scope of variables. Here is an example of how encapsulation can be used in JavaScript:

class BankAccount {   constructor(balance) {     this._balance = balance;   }   deposit(amount) {     this._balance += amount;   }   withdraw(amount) {     if (amount > this._balance) {       console.log("Funds are insufficient");     } else {       this._balance--= amount;     }   }   get balance() {     return this._balance;   } } let account = new BankAccount(2000); console.log(account.balance); // 2000 account.withdraw(1000); console.log(account.balance); // 1000
Code language: JavaScript (javascript)

Private and public properties and methods

In object-oriented programming (OOP), private properties can only be accessed within the object itself, while public properties can be accessed outside the object.

Private properties, which can only be accessed within the object itself, are typically used within methods to store internal states or to perform internal operations. For example, private property may be used to keep track of the method call or to store intermediate results during the execution of a method.

On the other hand, Public properties can be accessed from outside the object. They can be used within methods to expose the state or behavior of the object to other objects and to allow objects to interact with one another.

Advanced Concepts

Abstract classes and interfaces

To reiterate, an abstract class cannot be instantiated yet serves as the foundation for other classes. It defines a standard interface for a group of related classes but leaves the implementation of specific methods to the subclasses. An abstract class may have both abstract and concrete methods. 

An interface in object-oriented programming (OOP) is a contract for a group of related classes that defines a set of methods and properties the classes must implement. It specifies the structure and behavior that a class must have but does not provide any implementation details.

Interfaces are used to ensure that a class conforms to a certain standard and to provide a consistent way of interacting with objects of different classes. They also provide a level of abstraction, allowing objects to be treated as instances of a common interface, regardless of their actual class.


Mixins are a technique in object-oriented programming (OOP) that allows for the reuse of class behavior across multiple classes. A mixin is a class that defines a specific set of methods and properties that can be added to other classes.

Mixins are often used to provide a way to share common functionality across different classes without the need for a standard base class or complex class hierarchies. 

Prototypal Inheritance

Prototypal inheritance is a mechanism in object-oriented programming (OOP) that allows an object to inherit properties and methods from another object, called its prototype.

It is a way to create new objects based on existing objects and allows for a more dynamic and flexible way of organizing and structuring code compared to class-based inheritance.

ES6 Class Syntax

ES6 (ECMAScript 6) introduced a new syntax for creating classes in JavaScript, which provides a more familiar and class-based way of creating objects and managing an inheritance.

The new class syntax is built on top of JavaScript’s existing prototypal inheritance mechanism, but it provides a more straightforward and consistent way of creating and managing objects.

The syntax for declaring a class 

class NameOfClass {   }
Code language: JavaScript (javascript)

Use Cases

Creating reusable objects

Creating reusable objects in object-oriented programming (OOP) is a way to write efficient, maintainable, and modular code by creating objects that can be easily reused in multiple places in an application.

There are several ways to create reusable objects in JavaScript. Modules are one popular solution; they are JavaScript files that may be imported into the program and utilized elsewhere to provide specific functionality.

Managing complexity in large codebases

Managing complexity in large codebases is a challenging task in software development, as it requires finding ways to organize and structure code in an easy way to understand, maintain, and extend. Several techniques and best practices can be used to manage complexity in large codebases. Modular design allows developers to focus on a tiny piece of functionality simultaneously, making it easier to understand and maintain.

Object-oriented design patterns

There are several popular object-oriented design patterns, including:

The Model-View-Controller (MVC) pattern separates data management, user interface, and control flow into three distinct components: the model, the view, and the controller.

The Observer pattern

This pattern allows objects to register and receive notifications from other objects, allowing for a loosely coupled relationship between the objects.

Creating maintainable and scalable code

Creating maintainable and scalable code is essential to software development, ensuring that the codebase can be easily understood, modified, and extended over time. Several best practices and techniques can be used to create maintainable and scalable code. One of the most important best practices is a modular design, which involves breaking down a large codebase into smaller, self-contained modules. 


Summary of key points

In conclusion, the foundation of object-oriented JavaScript is the idea of objects, which are specific examples of classes that contain data and behavior. JavaScript is a prototypal language that uses prototypal inheritance as its primary mechanism for OOP. ES6 introduced class syntax, built on JavaScript’s existing prototypal inheritance mechanism. It provides a more straightforward and consistent way of creating and managing objects. 

Additional resources for learning OOP in JavaScript

Here are several options that can teach you JavaScript OOP:

“JavaScript: Understanding the Weird Parts” by Anthony Alicea 

“Object-Oriented JavaScript” by Stoyan Stefanov 

“Learning JavaScript Design Patterns” by Addy Osmani

Future of OOP in JavaScript

The future of OOP in JavaScript will continue to evolve with the introduction of new features, enhancements, and technologies. While JavaScript is primarily an object-oriented language, there has been a growing trend toward using functional programming techniques in recent years. With the inclusion of class syntax in ES6, JavaScript has become more similar to an OOP model based on classes.

Frequently Asked Questions to resolve (FAQs)

What are the object-oriented concepts in JavaScript?

Encapsulation: OOP allows you to hide the internal state and behavior of objects, which can provide a way to protect data.

Inheritance: OOP lets you take the properties and methods of a parent object and put them on a child object.

Polymorphism: Objects can take on various forms due to OOP.

Abstraction: OOP allows you to abstract away from the implementation details of an object and focus on its behavior.

What is an object of javascript? Explain with an example.

An object is a unique collection of related data and methods representing a single thing or notion in JavaScript.

class Human { //code } //object creation let human1 = new Human();
Code language: JavaScript (javascript)

What are the four basics of OOP?

The Four basics of OOP are Encapsulation, Abstraction, Polymorphism, and Inheritance.

How long does it take to learn OOP Javascript?

If you have past programming expertise and are familiar with the fundamental ideas of OOP, learning OOP in JavaScript may take a few weeks to a few months. But if you are new to programming, understanding OOP in JavaScript may take longer.

Why is Javascript object-oriented?

Because it is founded on the concept of objects, which are instances of classes that encapsulate data and action, JavaScript is an object-oriented language. Additionally, its built-in support for prototypes and first-class functions allows for creating powerful abstractions that can be used to create objects with complex behavior.

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