Inheritance (extends) and Implementing an Interface (implements)

This lesson covers class inheritance (extends) and implementing an interface with implements. It's for anyone searching "TypeScript extends implements difference."

extends creates a new class that inherits an existing class's functionality. implements, on the other hand, makes a class promise to honor the "shape" defined by an interface.

The example inherits class Animal with class Dog extends Animal, and also guarantees "has a sound" by having it implements an interface Soundable.

A common early mistake is forgetting to call super() in the subclass. Skip the super() call, which runs the parent class's constructor, and you get a compile error.

In real projects, a common combination is inheriting a class with a shared trait, like "animal," while expressing a specific ability, like "makes a sound" or "can fly," through an interface.

📖 Reference code

interface Soundable {
  speak(): string;
}

class Animal {
  constructor(public name: string) {}
}

class Dog extends Animal implements Soundable {
  speak(): string {
    return `${this.name}: Woof!`;
  }
}

const dog = new Dog("Rex");
console.log(dog.speak());

✍️ Your code

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