data1 = {};

handler = {

  get: (target, prop) => (target[prop]),

  set: (target, prop, value) => (target[prop] = value),

};

proxy = new  Proxy(data1, handler);

data2 = {

  get test() {

    return this._test;

  },

  set test(value) {

    return this._test = value;

  }

};

const EVENTS = new WeakMap();

function pub(object, event, data) {

  if (!EVENTS.has(object)) { return; }

  const callbacks = EVENTS.get(object)[event];

  if (callbacks) {

    for (const callback of callbacks) {

      callback(data);

    }

  }

}

function sub(object, event, callback) {

  let dict;

  if (!EVENTS.has(object)) {

    EVENTS.set(object, dict={});

  } else {

    dict = EVENTS.get(object);

  }

  let evList;

  if (event in dict) {

    (evList = dict[event]).push(callback);

  } else {

    evList = dict[event] = [callback];

  }

  return function unsub() {

    evList.splice(evList.indexOf(callback), 1);

  }

}

data3 = {};

sub(data3, 'set-test', v => data3.test = v);

sub(data3, 'get-test', () => pub(data3, 'getting-test', data3.test));

sub(data3, 'getting-test', v => a += v);

var a = 0;

data4 = {};

data5 = {};

sub(data5, 'set-test', v => { data5.test = v; pub(data5, 'getting-test', data3.test); });

sub(data5, 'getting-test', v => a += v);