How to solve this bug (JS)

Question

ES6 classes bug

https://www.sololearn.com/post/408067/?ref=app
https://code.sololearn.com/WM7C1cfqh937/?ref=app

Answer 1

I'm not getting the error shown in image but try enabling strict mode as said in error message.

Just place "use strict" string at top of your script :

"use strict";

class Rectangle {
......

Answer 2

The output is 5
What do you want output to be?