Private properties using Object.defineProperty and the .caller property of functions

private.js

function $private(object, property, descriptor) {
  var getter = descriptor.get;
  var setter = descriptor.set;

  var value = descriptor.default;

  var enumerable = Boolean(descriptor.enumerable) || false;
  var configurable = Boolean(descriptor.configurable) || false;

  var $descriptor = {
    __proto__: null,
    enumerable: enumerable,
    configurable: configurable
  };

  if (getter) $descriptor.get = function $get() {
    if (assertCalledBy(getter, $get)) {
      return value;
    }
  };

  if (setter) $descriptor.set = function $set(newValue) {
    if (assertCalledBy(setter, $set)) {
      value = newValue;
    }
  };

  return Object.defineProperty(object, property, $descriptor);

  function assertCalledBy(caller, f) {
    if (f.caller === caller) return true;
    throw new Error('Unauthorized access to the private \'' + property + '\' property');
  }
}