What’s the Difference Between ‘extends’ and ‘implements’ in TypeScript ?

In TypeScript, extends and implements are primarily used to define relationships between types and classes. In this article, we will learn the difference between ‘extends’ and ‘implements’ in TypeScript.

Extends

extends is used to create a subclass that inherits properties and methods from another class or to extend a type by including properties from another type.

Syntax (For class inheritance):

class DerivedClass extends BaseClass {
  // Additional properties and methods in the derived class
}

Syntax (For type extension):

type ExtendedType = BaseType & {
  // Additional properties and methods in the extended type
};

Example 1: In this example, we are using extends for class inheritance

Javascript

class Animal {
    makeSound(): void {
        console.log('Dog sound');
    }
}
// Derived class representing a
// specific type of animal: Dog
class Dog extends Animal {
    bark(): void {
        console.log('Dog is barking!');
    }
}

const myDog = new Dog();
myDog.makeSound();
myDog.bark();

Output:

Dog sound
Dog is barking!

Example 2: In this example, we are using extends for type extension.

Javascript

type Shape = {
    color: string;
};

type Square = Shape & {
    sideLength: number;
};
const mySquare: Square = {
    color: 'red',
    sideLength: 5,
};
console.log(mySquare);

Output:

{ color: 'red', sideLength: 5 }

Implements

Implements is used in a class to indicate that the class is going to implement a particular interface. It ensures that the class includes all the properties and methods specified by the interface.

Syntax:

class ClassName implements InterfaceName {
  // Class properties and methods
}

Example: In this example, the GFG class implements the GeeksForGeeks interface, and it is required to provide an implementation for the print method specified by the interface.

Javascript

interface GeeksforGeeks {
    print(): void;
}

class GFG implements GeeksforGeeks {
    print() {
        console.log('GeeksForGeeks');
    }
}
const output = new GFG();
output.print();

Output:

GeeksForGeeks

Difference between extends and implements

Features	extends	Implements
Inheritance	Extends is used for class inheritance. It allows a class to inherit properties and methods from another class.	Implements is used for interface implementation. It enables a class to provide specific implementations for the methods defined in an interface.
Multiple Inheritance	A class can extend only one class	A class can implement multiple interfaces
Implementation of Methods	No direct implementation of methods.	Requires the class to provide concrete implementations for all methods declared in the interface.
Code Reusability	Promotes code reusability	Promotes code reusability and abstraction through interfaces.
Abstract Classes	Can extend abstract classes	Cannot extend abstract classes but can implement abstract methods.