text: function _classCallCheck(instance, Constructor) {
      if (!(instance instanceof Constructor)) {
          throw new TypeError("Cannot call a class as a function");
      }
  }
  var A = function A() {
      "use strict";
      _classCallCheck(this, A);
      _field.set(this, {
          writable: true,
          value: 10
      });
      _uninitialized.set(this, {
          writable: true,
          value: void 0
      });
  };
  var _field = new WeakMap();
  var _uninitialized = new WeakMap();
  