Does Child Class Inherited their parent class prototype in the following example (JS)

Question

the follwoing code:

class Rectangle {
    constructor(w, h) {
        this.w = w;
        this.h = h;
    }
}

Rectangle.prototype.area = function () {
  return (this.w * this.h);  
};

class Square extends Rectangle {
    constructor(w, h) {
        super(w,  h);
        // this.w = w;
        // this.h = h;
    }
}

Do I have problems with my inheritance?

I'm trying to use:

const rec = new Rectangle(3, 4);

const sqr = new Square(3);

console.log(rec.area());

console.log(sqr.area());

rec prints the correct answer but sqr print's out: NaN

I also tried maybe adding a Square prototype:

Square.prototype.area = function () {
  return (this.w * this.w);  
};

but the output is:

-1  
-1 

so this also affected area for rec.area()

Answer 1

Since the Square constructor will be called with only one argument (since its size is equal at all sides), you need to "translate" this to a Rectangle constructor call that needs 2 arguments (width and height). Since both are equal for the square, you need to pass that single argument twice to the Rectangle constructor:

 class Rectangle { constructor(w, h) { this.w = w; this.h = h; } area() { // Use this notation for prototype methods return this.w * this.h; } }; class Square extends Rectangle { constructor(w) { // One argument... super(w, w); // ...Two arguments, but width == height } } let square = new Square(10); console.log(square.area());