How do I use class syntax for inheritance in JavaScript?

How do I use class syntax for inheritance in JavaScript?

In JavaScript, you can use the class keyword to create a class and the extends keyword to inherit from another class. For example:

class Animal {
    constructor(name) {
        this.name = name;
    }
    speak() {
        console.log(`${this.name} makes a noise.`);
    }
}

class Dog extends Animal {
    speak() {
        console.log(`${this.name} barks.`);
    }
}

const dog = new Dog('Rex');

dog.speak(); // Rex barks.

Can you explain how the super keyword works in this context?

Certainly! The super keyword is used to call functions on an object's parent class. In the context of inheritance, you can use super() in the constructor of a derived class to call the constructor of the parent class. Here's an example:

class Dog extends Animal {
    constructor(name, breed) {
        super(name); // Calls the constructor of Animal
        this.breed = breed;
    }
    speak() {
        console.log(`${this.name} barks. I am a ${this.breed}.`);
    }
}

const dog = new Dog('Rex', 'Golden Retriever');

dog.speak(); // Rex barks. I am a Golden Retriever.

What happens if I don't call super() in the derived class constructor?

If you don't call super() in the constructor of a derived class, you will get a ReferenceError because this is not defined until super() is called. It's mandatory to call super() before you can use this in the derived class.