Is a method added to prototype of class available in inherited class?

Question

I am pretty new to Javascript and started a few days ago. When I was doing practice, I have encountered a problem, even though I did extensive research I did not still get it.

I am given the following Rectangle class definition

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

I am asked to add the method area() through prototyping and I did the following:

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

And if I inherit the Rectangle class for Square class, does the square class's instance inherit area() method which is added through prototyping? Like this?

class Square extends Rectangle{
    constructor(w, h){
        super(w, h);
    }
} 

Given the following code above, is it possible or how to call method area() from Square instance so that following code works?

const sqr = new Square(3);   
console.log(sqr.area());

If you are familiar with other languages, what prototyping can be compared to other languages such as Java, Kotlin and etc?

Answer 1

There's a problem in the constructor for your Square class. It should only accept one argument.

After correcting that, it works fine:

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) {
    super(w, w);
  }
}

console.log(new Square(2).area());

For the second part of your question:

If you are familiar with other languages, what prototyping can be compared to other languages such as Java, Kotlin and etc?

I think this answer summarizes the differences between classical inheritance (e.g. Java) and prototypal inheritance (e.g. JavaScript) well.