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How to use Interface with Class in TypeScript ?

Last Updated : 23 Jan, 2025
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In TypeScript, interfaces define the structure that classes must adhere to, ensuring consistent object shapes and facilitating type-checking.

  • Interfaces declare properties and methods without implementations, serving as contracts for classes to implement.
  • Classes use the implements keyword to adhere to an interface, providing concrete implementations for the declared members.

These are the following methods:

1. Interface Implemented by Class

In TypeScript, a class can implement an interface to ensure it adheres to a specific structure defined by the interface.

Syntax:

class ClassName implements InterfaceName {
  // Class properties and methods
}
JavaScript 
interface Shape {   calculateArea(): number; }  class Rectangle implements Shape {   width: number;   height: number;    constructor(width: number, height: number) {     this.width = width;     this.height = height;   }    calculateArea(): number {     return this.width * this.height;   } }  const rect = new Rectangle(5, 10); console.log(rect.calculateArea());
  • The Shape interface defines a contract with the calculateArea method.
  • The Rectangle class implements the Shape interface, providing concrete implementations for the calculateArea method.
  • An instance of Rectangle is created with a width of 5 and a height of 10, and the calculateArea method is called to compute the area.

Output:

50

2. Multiple Interfaces Implemented by Class

In TypeScript, a class can implement multiple interfaces, allowing it to adhere to multiple contracts and ensuring it provides implementations for all the specified members.

Syntax:

class ClassName implements Interface1, Interface2 {
  // Class properties and methods
}
JavaScript 
interface Shape {   calculateArea(): number; }  interface Color {   color: string; }  class Circle implements Shape, Color {   radius: number;   color: string;    constructor(radius: number, color: string) {     this.radius = radius;     this.color = color;   }    calculateArea(): number {     return Math.PI * this.radius * this.radius;   } }  const circle = new Circle(5, 'red'); console.log(`Color: ${circle.color}`); console.log(`Area: ${circle.calculateArea()}`);
  • The Shape interface declares a calculateArea method, defining a contract for calculating the area of a shape.
  • The Color interface includes a color property, specifying that any implementing class should have a color attribute.
  • The Circle class implements both Shape and Color interfaces, providing concrete implementations for the calculateArea method and the color property.

Output:

Color: red
Area: 78.53981633974483

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Article Tags :
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  • Web Technologies
  • TypeScript

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