Classes in TypeScript

A typed class

Declare each property's type, then assign values in the constructor.

class Dog {
  name: string;
  age: number;

  constructor(name: string, age: number) {
    this.name = name;
    this.age = age;
  }

  bark(): string {
    return `${this.name} says Woof!`;
  }
}

const rex = new Dog("Rex", 3);

Implementing an interface

implements makes TS check that the class actually provides everything the interface promises.

interface Speaker {
  speak(): string;
}

class Cat implements Speaker {
  speak(): string {
    return "Meow!";
  }
}
// If speak() were missing:
// Error: Class 'Cat' incorrectly implements interface 'Speaker'.

Classes are structural too

A class doesn't need implements to satisfy an interface — if its shape matches, TS accepts it anywhere that interface is expected.