TypeScript - interface extends keyword

In TypeScript it is possible to extend interface in following way.

1. extends keyword example

interface Shape {
    getName() : string;
}

interface Square extends Shape {
    computePerimeter(a : number, b : number) : number;
    computeArea(a : number, b : number) : number;
}

class LocalSquare implements Square {
    public getName() : string {
        return 'Square';
    }

    public computePerimeter(a : number, b : number) : number {
        return 2 * a + 2 * b;
    }
    
    public computeArea(a : number, b : number) : number {
        return a * b;
    }
}

let square = new LocalSquare();

console.log(square.getName());
console.log(square.computePerimeter(2, 3));
console.log(square.computeArea(2, 3));

Output:

Square
10
6

Run it online here. 

Note: Square interface extends Shape interface.

Merged questions

• TypeScript - interface inheritance with practical code example

References

• Extending Interfaces - Microsoft Docs