Javascript OOP Classes are not real-- it is just syntactic sugar!

class MyBaseClass {

    constructor(thingOne, thingTwo) {

        this.thingOne = thingOne;

        this.thingTwo = thingTwo;

    }

    getThingOne() {

        return this.thingOne;

    }

    getThingTwo {

        return this.thingTwo;

    }

}

class MyExtendedClass extends MyBaseClass {

    constructor(thingOne, thingTwo, thingThree) {

        super(thingOne, thingTwo);

        this.thingThree = "thingThree"

    }

    getThingThree() {

        return this.thingThree;

    }

}

let theThings = new MyExtendedClass("foo", "bar", "baz");

This is the helper way to write the following:

function MyBaseClass (thingOne, thingTwo) {

    let newMyBaseClass = Object.create(myBaseClassConstructor);

    newMyBaseClass.thingOne = thingOne;

    newMyBaseClass.thingTwo = thingTwo;

    return newMyBaseClass;

}

let myBaseClassConstructor = {

    getThingOne: function() {

        return this.thingOne;

    },

    getThingTwo: function() {

        return this.thingTwo;

    }

}

function MyExtendedClass(thingOne, thingTwo, thingThree) {

    let newMyExtendedClass = MyBaseClass(thingOne, thingTwo);

    Object.setPrototypeOf(newMyExtendedClass, myExtendedClassConstructor);

    newMyExtendedClass.thingThree = thingThree;

    return newMyExtendedClass;

}

let myExtendedClassConstructor = {

    getThingThree: function() {

        return this.thingThree;

    }

}

Object.setPrototypeOf(myExtendedClassConstructor, myBaseClassConstructor);

const theSquare = MyBaseClass(2,3);

theSquareArea = theSquare.getThingOne() * theSquare.getThingTwo();

const theBox = MyExtendedClass(2, 3, 5);

theCubicVolume = theBox.getThingOne() * theBox.getThingTwo() * theBox.getThingThree();