super in javascirpt

1class Rectangle {
2  constructor(height, width) {
3    this.name = 'Rectangle';
4    this.height = height;
5    this.width = width;
6  }
7  sayName() {
8    console.log('Hi, I am a ', this.name + '.');
9  }
10  get area() {
11    return this.height * this.width;
12  }
13  set area(value) {
14    this._area = value;
15  }
16}
17
18class Square extends Rectangle {
19  constructor(length) {
20    this.height; // ReferenceError, super needs to be called first!
21
22    // Here, it calls the parent class's constructor with lengths
23    // provided for the Rectangle's width and height
24    super(length, length);
25
26    // Note: In derived classes, super() must be called before you
27    // can use 'this'. Leaving this out will cause a reference error.
28    this.name = 'Square';
29  }
30}