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Difference between TypeScript Class and Interface

Class

TypeScript is an object-oriented JavaScript language, which supports programming features like classes, interfaces, polymorphism, data-binding, etc. TypeScript support these features from ES6 and later version.

Classes are the fundamental entities which are used to create reusable components. It is a group of objects which have common properties. In terms of OOPs, a class is a template or blueprint for creating objects. It is a logical entity.

We can define the following properties in a class definition:

Fields: It is a variable declared in a class.
Methods: It represents an action for the object.
Constructors: It is responsible for initializing the object in memory.
Nested class and interface: It means a class can contain another class.

Syntax to declare a class

We can declare a class by using the class keyword in TypeScript. The following syntax explains the class declaration.

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Interface

An Interface is a structure which acts as a contract in our application. It defines the syntax for classes to follow, means a class which implements an interface is bound to implement all its members. We cannot instantiate the interface, but it can be referenced by the class object that implements it.

The interface contains only the declaration of the methods and fields, but not the implementation. We cannot use it to build anything. A class inherits an interface, and the class which implements interface defines all members of the interface.

When the Typescript compiler compiles it into JavaScript, then the interface will be removed from the JavaScript file. Thus, its purpose is to help in the development stage only.

Interface Declaration

We can declare an interface by using the interface keyword in TypeScript. The following syntax explains the interface declaration.

Use of Interface

We can use the interface for the following things:

• Validating the specific structure of properties
• Objects passed as parameters
• Objects returned from functions.

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TypeScript class vs. TypeScript Interface

	TypeScript Class	TypeScript Interface

Introduction Classes are the fundamental entities used to create reusable components. It is a group of objects which have common properties. It can contain properties like fields, methods, constructors, etc. An Interface defines a structure which acts as a contract in our application. It contains only the declaration of the methods and fields, but not the implementation. Usage It is used for object creation, encapsulation for fields, methods. It is used to create a structure for an entity. Keyword We can create a class by using the class keyword. We can create an interface by using the interface keyword. Compilation A class cannot disappear during the compilation of code. Interface completely disappeared during the compilation of code. Real-Time Usage Design Pattern, Designing project Structure Implements of defined Architectures Instantiation A class can be instantiated to create an object. An interface cannot be instantiated. Methods The methods of a class are used to perform a specific action. The methods in an interface are purely abstract (the only declaration, not have a body). Access Specifier The member of a class can be public, protected, or private. The members of an interface are always public. Constructor A class can have a constructor. An interface cannot have a constructor. Implement/Extend A class can extend only one class and can implement any number of the interface. An interface can extend more than one interfaces but cannot implement any interface.