What is New in JavaScript?

What is a New Keyword?

In JavaScript, the new keyword is used to create an instance of an object with the use of the constructor method. It means when we create a new instance, JavaScript calls the constructor method every time we create an instance.

In simple words, the new keyword helps us to create an instance of the object that has a constructor method. With the use of a new keyword, users can create instances of user-defined as well as built-in object types. We can create instances of classes, prototypes, or constructor methods.

In JavaScript, when we create a function with new keyword the function is used as constructor. The new keyword will do the following:

• First, it will create an empty JavaScript object.
• After that, it will set its prototype for inheritance.
• The 'this' variable is made to point to the newly created object. It helps us to bind the property that is declared with this keyword to the new object.
• It also executes the constructor method using new created object whenever it is used.
• It returns a newly created object unless the constructor function returns a non-null object reference.

Syntax

Parameter

Constructor: In JavaScript, it is the name of the constructor method or class name.

Argument: In JavaScript, there can be multiple arguments to initialize the object properties with them.

Using the 'new' keyword with Function Constructor

In JavaScript, to use a function as a constructor, we should call the function while a new keyword is placed before the function name.

In JavaScript, we can also define multiple objects with the use of a function constructor. The constructor method works as the object's prototype.

Syntax:

The syntax of the new keyword and constructor function are as follows:

Example

Explanation

In the above example, we defined the Watch() constructor function. The watch() constructor function initializes the brand, price, and type properties. Then, we created two new instances of the Watch() function and printed them in the output.

Output:

 The rolex object is: {"brand":"Rolex","price":40000,"type":"analog"} The sonata object is: {"brand":"sonata","price":3000,"type":"digital"} 

Using 'new' keyword with Class

In JavaScript, we can also use the new keyword to define the instance of a class. When we use the new keyword with the class, it provides the blueprint for the object.

Before ES6, constructor functions defined object templates; after ES6, classes are used instead.

Example

Explanation

In the above example, we have defined the 'WindowClass class'. In this 'WindowClass' we have added the constructor to initialize the properties. We have also added the getDetails() method in the class.

After that, we used the new keyword followed by the class name to define an object of the WindowClass.

Output:

 Color: Red Size: large Type: wooden 

Using 'new' keyword with a built-in object

We can also use the new keyword to define the instance of the built-in object having a constructor function.

Syntax

In the above syntax, we have passed the numeric value as an argument of the Number() constructor.

Example

Output:

 num = 10, typeof num object str = Hello, typeof str object 

The purpose of the new keyword in JavaScript

Creating a new object

In JavaScript, the new keyword is used to create a new instance of an object. When we call a constructor function with new, it creates the object.

Example

Setting the prototype

In JavaScript, the new object's internal [[Prototype]] property is set to the constructor functions prototype property. It allows the new object to inherit the properties and methods from the constructor's prototype.

Binding this to the new object

In JavaScript, inside the constructor function, `this` refers to the new object that is being created. It also allows us to add the properties and methods to the new object.

Returning the new object

The 'new' Keyword in JavaScript implicitly returns the object created by the constructor function. Now, If the constructor function explicitly returns an object, that object will be returned instead.

Conclusion

In JavaScript, the new keyword is a fundamental tool for object creation and plays a crucial role in the language's object-oriented capabilities. By invoking a constructor function or class with new, you generate a new object instance with its own properties and methods, adhering to the blueprint defined by the constructor. This process involves setting up the prototype chain, binding this context to the new object, and handling the return of the created object.