SquirrelGuy-5 Classes don't work in code.org but a lot of their functionality can be reconstructed by making a function which returns an object:
class Rect {
    constructor(w,h) {
        this.w = w;
        this.h = h;
    }
    area() {
        return this.w * this.h;
    }
}
is basically the same as
function Rect(w,h) {
    var obj = {};
    obj.w = w;
    obj.h = h;
    obj.area = function() { 
        return this.w * this.h;
    }
}