Interfaces

Interfaces

An interface defines the shape of an object — what properties it must have and their types:

interface Point {
    x: number;
    y: number;
}

const origin: Point = { x: 0, y: 0 };
const p: Point = { x: 3, y: 4 };

TypeScript checks that the object has all required properties with the correct types:

const bad: Point = { x: 1 };         // Error: missing 'y'
const bad2: Point = { x: "1", y: 2 }; // Error: 'string' not assignable to 'number'

Using Interfaces as Parameters

Interfaces shine as function parameter types:

function distance(p: Point): number {
    return Math.sqrt(p.x * p.x + p.y * p.y);
}

console.log(distance({ x: 3, y: 4 }));  // 5

Nested Interfaces

interface Rectangle {
    topLeft: Point;
    bottomRight: Point;
}

Your Task

Define an interface Person with name: string and age: number. Write function introduce(p: Person): string that returns "Hi, I'm [name] and I'm [age] years old".