Introduction to Object Oriented Programming in JavaScript

06 Jul, 2022
As JavaScript is widely used in Web Development, in this article we will explore some of the Object Oriented mechanisms supported by JavaScript to get the most out of it. Some of the common interview questions in JavaScript on OOPS include,- “How is Object-Oriented Programming implemented in JavaScript? How does it differ from other languages? Can you implement Inheritance in JavaScript” and so on...
There are certain features or mechanisms which makes a Language Object-Oriented like: 
Object
Classes
Encapsulation
Inheritance
Let’s dive into the details of each one of them and see how they are implemented in JavaScript.
1. Object– An Object is a unique entity that contains properties and methods. For example “car” is a real life Object, which has some characteristics like color, type, model, horsepower and performs certain actions like drive. The characteristics of an Object are called Properties in Object-Oriented Programming and the actions are called methods. An Object is an instance of a class. Objects are everywhere in JavaScript, almost every element is an Object whether it is a function, array, or string. 
Note: A Method in javascript is a property of an object whose value is a function. 
Object can be created in two ways in JavaScript: 
Using an Object Literal 
Javascript
//Defining objectlet person = {    first_name:'Mukul',    last_name: 'Latiyan',     //method    getFunction : function(){        return (`The name of the person is          ${person.first_name} ${person.last_name}`)    },    //object within object    phone_number : {        mobile:'12345',        landline:'6789'    }}console.log(person.getFunction());console.log(person.phone_number.landline);
Output: 
Using an Object Constructor: 
Javascript
//using a constructorfunction person(first_name,last_name){   this.first_name = first_name;   this.last_name = last_name;}//creating new instances of person objectlet person1 = new person('Mukul','Latiyan');let person2 = new person('Rahul','Avasthi'); console.log(person1.first_name);console.log(`${person2.first_name} ${person2.last_name}`);
Output: 
Using Object.create() method: The Object.create() method creates a new object, using an existing object as the prototype of the newly created object. 
Javascript
// Object.create() example a// simple object with some propertiesconst coder = {    isStudying : false,    printIntroduction : function(){        console.log(`My name is ${this.name}. Am I          studying?: ${this.isStudying}.`)    }}// Object.create() methodconst me = Object.create(coder); // "name" is a property set on "me", but not on "coder"me.name = 'Mukul'; // Inherited properties can be overwrittenme.isStudying = true; me.printIntroduction();
Output: 
2. Classes– Classes are blueprint of an Object. A class can have many Objects because class is a template while Object are instances of the class or the concrete implementation. Before we move further into implementation, we should know unlike other Object Oriented Language there are no classes in JavaScript we have only Object. To be more precise, JavaScript is a prototype based Object Oriented Language, which means it doesn’t have classes, rather it defines behaviors using a constructor function and then reuse it using the prototype. 
Note: Even the classes provided by ECMA2015 are objects.
JavaScript classes, introduced in ECMAScript 2015, are primarily syntactical sugar over JavaScript’s existing prototype-based inheritance. The class syntax is not introducing a new object-oriented inheritance model to JavaScript. JavaScript classes provide a much simpler and clearer syntax to create objects and deal with inheritance. –Mozilla Developer Network
Example: Lets use ES6 classes then we will look at the traditional way of defining an Object and simulate them as classes.
Javascript
// Defining class using es6class Vehicle {  constructor(name, maker, engine) {    this.name = name;    this.maker =  maker;    this.engine = engine;  }  getDetails(){      return (`The name of the bike is ${this.name}.`)  }}// Making object with the help of the constructorlet bike1 = new Vehicle('Hayabusa', 'Suzuki', '1340cc');let bike2 = new Vehicle('Ninja', 'Kawasaki', '998cc'); console.log(bike1.name);    // Hayabusaconsole.log(bike2.maker);   // Kawasakiconsole.log(bike1.getDetails());
Output:
Traditional Way.
Javascript
// Defining class in a Traditional Way.function Vehicle(name,maker,engine){    this.name = name,    this.maker = maker,    this.engine = engine}; Vehicle.prototype.getDetails = function(){    console.log('The name of the bike is '+ this.name);} let bike1 = new Vehicle('Hayabusa','Suzuki','1340cc');let bike2 = new Vehicle('Ninja','Kawasaki','998cc'); console.log(bike1.name);console.log(bike2.maker);console.log(bike1.getDetails());
Output: 
As seen in the above example it is much simpler to define and reuse objects in ES6. Hence, we would be using ES6 in all of our examples.
3. Encapsulation – The process of wrapping properties and functions within a single unit is known as encapsulation. Let’s understand encapsulation with an example.
Javascript
//encapsulation exampleclass person{    constructor(name,id){        this.name = name;        this.id = id;    }    add_Address(add){        this.add = add;    }    getDetails(){        console.log(`Name is ${this.name},Address is: ${this.add}`);    }} let person1 = new person('Mukul',21);person1.add_Address('Delhi');person1.getDetails();
Output: 
In the above example we simply create a person Object using the constructor and Initialize its properties and use its functions. We are not bothered with the implementation details. We are working with an Object’s interface without considering the implementation details. Sometimes encapsulation refers to the hiding of data or data Abstraction which means representing essential features hiding the background detail. Most of the OOP languages provide access modifiers to restrict the scope of a variable, but their are no such access modifiers in JavaScript but there are certain ways by which we can restrict the scope of variables within the Class/Object. 
Example: 
Javascript
// Abstraction examplefunction person(fname,lname){    let firstname = fname;    let lastname = lname;     let getDetails_noaccess = function(){        return (`First name is: ${firstname} Last            name is: ${lastname}`);    }     this.getDetails_access = function(){        return (`First name is: ${firstname}, Last            name is: ${lastname}`);    }}let person1 = new person('Mukul','Latiyan');console.log(person1.firstname);console.log(person1.getDetails_noaccess);console.log(person1.getDetails_access());
Output: 
In the above example we try to access some property(person1.firstname) and functions(person1.getDetails_noaccess) but it returns undefined while their is a method which we can access from the person object(person1.getDetails_access()). By changing the way we define a function we can restrict its scope.
4. Inheritance – It is a concept in which some properties and methods of an Object are being used by another Object. Unlike most of the OOP languages where classes inherit classes, JavaScript Objects inherit Objects i.e. certain features (property and methods) of one object can be reused by other Objects. 
Let’s understand inheritance with an example: 
Javascript
//Inheritance exampleclass person{    constructor(name){        this.name = name;    }    //method to return the string    toString(){        return (`Name of person: ${this.name}`);    }}class student extends person{    constructor(name,id){        //super keyword for calling the above class constructor        super(name);        this.id = id;    }    toString(){        return (`${super.toString()},Student ID: ${this.id}`);    }}let student1 = new student('Mukul',22);console.log(student1.toString());
Output: 
In the above example, we define an Person Object with certain properties and methods and then we inherit the Person Object in the Student Object and use all the properties and methods of the person Object as well as define certain properties and methods for the Student Object. 
Note: The Person and Student object both have same method (i.e toString()), this is called Method Overriding. Method Overriding allows a method in a child class to have the same name and method signature as that of a parent class. In the above code, the super keyword is used to refer to the immediate parent class’s instance variable. 
In this article we introduced Object Oriented features in JavaScript, there is an entire book that explains Object-Oriented Programming in JavaScript in great details,- ” Object-Oriented JavaScript by Stoyan Stefanov” This article is contributed by Sumit Ghosh. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
JavaScript is best known for web page development but it is also used in a variety of non-browser environments. You can learn JavaScript from the ground up by following this JavaScript Tutorial and JavaScript Examples.
 
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