Private object attributes using ES6 WeakMap

gistfile1.js

var My = (function() {
    var privates = new WeakMap;
    return function(a) {
        privates.set(this, a);
        this.setter = function(a) {
            privates.set(this, a)
        };
        this.getter = function() {
            return privates.get(this)
        };
    }
})()

my = new My(1)
console.log(my.getter());
my.setter(2)
console.log(my.getter());