Vanilla js class factory

I was trying to implement some kind of factory that create a class definition in the run time,I figure this work my code look like this

 function JsClassFactory() {
    this.X = class {

    };
    this.addMethod = (name, def) => {
        let Y = class extends this.X {
            constructor() {
                super()
                this[name] = def
            }
        }
        this.X = Y
        return this;
    }

    this.addAttribute = (name, def) => {
        this.addMethod(name, def)
    }

    this.getClass = function () {
        return this.X
    };
}


(function () {
    const cf = new JsClassFactory()
    cf.addAttribute('age', 35)
    cf.addAttribute('name', 'chehimi')

    cf.addMethod('myName', function () {
        console.log(' i am %s', this.name)
    })
    cf.addMethod('myAge', function () {
        console.log('my age is', this.age)
    })
    let z = new (cf.getClass())
    z.myName();
    z.myAge()
    cf.addAttribute('name', 'ali')
    cf.addAttribute('age', 15)
    let t = new (cf.getClass())
    t.myName();
    t.myAge()
})()

i am asking if there is a better a way to implement this feature?
or a better work arround,