code: function PromiseCapability(C) {
    var resolve, reject;
    this.promise = new C(function ($$resolve, $$reject) {
      if (resolve !== undefined || reject !== undefined) throw TypeError('Bad Promise constructor');
      resolve = $$resolve;
      reject = $$reject;
    });
    this.resolve = _aFunction(resolve);
    this.reject = _aFunction(reject);
  }
docs: 25.4.1.5 NewPromiseCapability(C)