Extending Interfaces

1. Welcome and Icebreaker:

• If you could extend any object in your life with new features, what would you add?

2. Outline the Session:

• We’ll learn how to extend interfaces in TypeScript to build on existing contracts.
• Learning Outcomes: Understand how to use extends to create more specific interfaces from general ones.
• Let’s build on our knowledge!

3. Concept Explanation:

• Extending Interfaces allows you to create new interfaces that inherit properties and methods from one or more existing interfaces.
• Use the extends keyword.
• This helps you build more specific types from general ones, promoting code reuse and flexibility.

4. Live Coding Demonstration:

interface Person {
  name: string;
}

interface Employee extends Person {
  employeeId: number;
}

const emp: Employee = {
  name: "Alice",
  employeeId: 123
};
console.log(emp);

// Extending multiple interfaces
interface A { a: number; }
interface B { b: string; }
interface C extends A, B {
  c: boolean;
}
const obj: C = { a: 1, b: "test", c: true };
console.log(obj);

5. Tasks:

• Short Exercise:
  1. Define an interface Shape with a property color (string).
  2. Define an interface Circle that extends Shape and adds a property radius (number).
  3. Create a variable of type Circle and print its properties.