TypeScript Interfaces Type

interface Employee {
    // The readonly-indicates id cannot be modified
    readonly id: number;
    firstName: string;
    lastName: string;
    age: number;
    //The ?-indicates city is a optional property
    city?: string
}

// Create an object adhering 
// to the Employee interface
const employee1: Employee = {
    id: 1,
    firstName: "John",
    lastName: "Doe",
    age: 30,
};

console.log(`Employee:First Name : ${employee1.firstName}
  ,Last Name : ${employee1.lastName},Age : ${employee1.age}`); 

interface Shape {
    color: string;
    area(): number;
}

interface Circle extends Shape {
    radius: number;
}

class CircleImpl implements Circle {
    constructor(public color: string,
        public radius: number) { }

    area(): number {
        return Math.PI * this.radius ** 2;
    }
}
const myCircle = new CircleImpl("red", 5);
console.log(`Color: ${myCircle.color},
 Area: ${myCircle.area()}`);

interface HybridProduct {
    readonly id: number;
    name: string;
    price: number;
    description?: string;
    validate(obj: any): boolean;
}

const HybridProduct: HybridProduct = {
    id: 0,
    name: '',
    price: 0,
    validate(obj: any): boolean {
        if (typeof obj.id !== 'number' || typeof obj.name !== 'string' || typeof obj.price !== 'number') {
            return false;
        }
        if (obj.description && typeof obj.description !== 'string') {
            return false;
        }
        return true;
    }
};

const product = {
    id: 1,
    name: "Laptop",
    price: 1500
};

console.log(`Product is valid: ${HybridProduct.validate(product)}`);