function Foo(x) {
    this.x = x;
    this.y = 432;
}
Foo.prototype.point = function() {
    return 'Foo(' + this.x + ', ' + this.y + ')';
}

var myfoo = new Foo(99);
console.log(myfoo.point()); // prints "Foo(99, 432)"


class Foo {
    constructor(x) {
        this.x = x;
        this.y = 432;
    }

    point() {
        return 'Foo(' + this.x + ', ' + this.y + ')';
    }
}

let myfoo = new Foo(99);
console.log(myfoo.point()); // prints "Foo(99, 432)"