aSymboler - A common interface for using symbol property values to create private keys.

gistfile1.txt

const s = new Proxy({},{
    get(target, prop){
        if(!target[prop]) target[prop] = Symbol();
        return target[prop];
    },
    set(){
        return false;
    }
})

var x = {};
x[s.a] = 6
console.log(x[s.a]);