getPropertyDescriptor.js

Object.getPropertyDescriptor || (Object.getPropertyDescriptor = function (obj, name) {
  var desc;
  while (obj) {
    desc = Object.getOwnPropertyDescriptor(obj, name);
    if (desc) {
      desc.configurable = true;
      return desc;
    }
    obj = Object.getPrototypeOf(obj);
  }
});