private member for js

README.md

import ns from "./namespace";

const internal = ns();

class ClassName {

    constructor() {
        
        internal(this).userName = "Foo";
        let userName = internal(this).userName;
        
    }

}

namespace.js

export default function namespace(){
    const map = new WeakMap();
    return (obj) => {
        if (!map.has(obj)) {
            map.set(obj, {});
        }
        return map.get(obj);
    };
}