JavaScript Object Constructors (original) (raw)

Last Updated : 18 Jan, 2025

An object is the collection of related data or functionality in the form of **key. These functionalities usually consist of several functions and variables. All JavaScript values are objects except primitives.

const GFG = {
subject : "programming",
language : "JavaScript",
}

Here, _subject and _language are the **keys and _programming and _JavaScript are the **values.

Object Constructor

A constructor function is a special type of function in JavaScript that is used to create and initialize objects. Constructors are used with the new keyword to create instances of a particular type (object). By using constructors, we can easily create multiple instances of the same type of object, all with their own unique properties and methods.

JavaScript ``

//Driver Code Starts{ // Constructor function //Driver Code Ends }

//Driver Code Starts{

//Creating Instances with a Constructor const p1 = new Person("Akash", 30); const p2 = new Person("Anvesh", 25);

p1.sayHello(); p2.sayHello(); //Driver Code Ends }

Output

My name is Akash and I am 30 years old. My name is Anvesh and I am 25 years old.

**this keyword

The **this keyword refers to the object it belongs to, like OOPs languages C++, C#, JAVA etc. **this keyword is used in different ways in different areas. While executing a function in JavaScript that has a reference to its current execution context, that is the reference by which the function or data member is called. See the previous example.

**Adding Property to an Object

The property can be added to the object by using **dot(.) operator or **square bracket.,

const GFG = {
articles: 'computer science',
quantity: 3000,
};

The **GFG has two properties “articles” and “quantity”. Now we wish to add one more property name called **subject.

Using dot (.) operator

GFG.subject: 'JavaScript';

Using square bracket:

GFG['subject']: 'JavaScript';

Here, **subject is the property and **‘JavaScript’ is the value of the property. **Adding a property to Constructor: We cannot add a property to an existing constructor like adding a property to an object (see previous point), for adding a property we need to declare under the constructor.

function GFG(a, b, c) {
this.A = a;
this.B = b;
this.C = c;
this.G = "GEEK";
}

Here, we add a property name **G with value **“GEEK”, in this case the value **“GEEK” is not passed as an argument.

**Adding a Method to an Object

We can add a new method to an existing object.

GFG.n = function () {
return this.A + this.B;
};

Here, the object is GFG.

**Adding a Method to Constructor

function GFG(a, b, c) {
this.A = a;
this.B = b;
this.C = c;
this.n = function () {
return this.A + this.B;
}
}

Here, in the last line a method is added to an object.

**Instantiating an object constructor

There are two ways to instantiate object constructor,

const object_name = new Object(); // or
const object_name = new Object("java", "JavaScript", "C#");

const object_name = { };

In 1st method, the object is created by using **new keyword like normal OOP languages, and **“Java”, “JavaScript”, “C#” are the arguments, that are passed when the constructor is invoked. In 2nd method, the object is created by using **curly braces “{ }”.

**Assigning properties to the objects: There are two ways to assigning properties to the objects.

**Using dot (.) operator:

object_name . properties = value;

**Using third bracket:

object_name [ 'properties'] = value;

**Example 1: Object creation by using **new keyword and assigning properties to the object using **dot(.) operator.

javascript `

let gfg = new Object();

gfg.a = "JavaScript"; gfg.b = "GeeksforGeeks";

//Driver Code Starts{ console.log("Subject: " + gfg.a); console.log("Author: " + gfg.b ); //Driver Code Ends }

Output

Subject: JavaScript Author: GeeksforGeeks

**Example 2: Object creation using **curly braces and assigning properties to the object using **third bracket “[]” operator.

javascript `

let gfg = { };

gfg['a'] = "JavaScript"; gfg['b']= "GeeksforGeeks";

//Driver Code Starts{ console.log("Subject: " + gfg.a); console.log("Author: " + gfg.b ); //Driver Code Ends }

Output

Subject: JavaScript Author: GeeksforGeeks

**Example 3: This example shows how to use function() with object constructor.

javascript `

let gfg = new Object();

gfg.a = "JavaScript"; gfg.b = "GeeksforGeeks"; gfg.c = function () { return (gfg.a +" "+ gfg.b); };

//Driver Code Starts{ console.log("Subject: " + gfg.a); console.log("Author: " + gfg.b); console.log("Adding the strings: "+ gfg.c() ); //Driver Code Ends }

Output

Subject: JavaScript Author: GeeksforGeeks Adding the strings: JavaScript GeeksforGeeks

**Example 4: Another way to create a function using function name.

javascript `

let gfg = { };

gfg.a = "JavaScript"; gfg.b = "GeeksforGeeks"; gfg.c = add;

// Declare function add() function add() { return (gfg.a +" "+ gfg.b); };

//Driver Code Starts{ console.log("Subject: " + gfg.a); console.log("Author: " + gfg.b); console.log("Adding the strings: "+ gfg.c()); //Driver Code Ends }

Output

Subject: JavaScript Author: GeeksforGeeks Adding the strings: JavaScript GeeksforGeeks