Sub class with ES6

ES6 introduces subclass syntax which is just an easy way to extends a class to another.

Subclass

When you create class you may have a class who have his own properties, methods but can also have the same than another class instead of rewrite all this methods or properties you can inherit this class with an other one.

class Person = {
    constructor(name, secondName, age) {
        this.name = name;
        this.familyName = secondName;
        this.age = age;
    }

    calculateAge() {
        return  new Date().getFullYear() - this.age;
    }

    eat() {
        return `${this.name} is eating`;
    }

    static hey() {
        return `Hello world`;
    }
};

class Athlete extends Person = {
    constructor(name, secondName, age, olympicGames, medals) {
        super(name, secondName, age);
        this.olympicGame = olympicGames;
        this.medal = medals;
    }

    action() {
        return `${ super.eat() } something`;
    }

    winMedals() {
        return this.medal++;
    }
}

1. To inherit a class to another you have to use the extends keyword and the name of the parent class here Person.
2. Like we declare a class we use the constructor function in order to define properties when we will create an object based on this class, so the parameters will be our new properties.
3. Inside the constructor function we have a new function super this function is used to access and call functions on an object parent she's necessary when you use inheritance with class and must be used directly inside the constructor function if you want be able tu use the this keyword inside this class.
4. In parameters you have to call all the properties and functions of the parent class, after that you can start to use the this keyword to define your own new properties.
5. As you may seen we created a new function inside the Athlete class and we use the super keyword to call the eat function of the Person class, you can also access to the functions parent with the super keywords which is this time not a function but an object.