deps/v8/src/js/promise.js
function NewPromiseCapability(C) {
  if (C === GlobalPromise) {
    // Optimized case, avoid extra closure.
    var promise = PromiseInit(new GlobalPromise(promiseRawSymbol));
    var callbacks = CreateResolvingFunctions(promise);
    return {
      promise: promise,
      resolve: callbacks.resolve,
      reject: callbacks.reject
    };
  }

  var result = {promise: UNDEFINED, resolve: UNDEFINED, reject: UNDEFINED };
  result.promise = new C((resolve, reject) => {
    if (!IS_UNDEFINED(result.resolve) || !IS_UNDEFINED(result.reject))
        throw MakeTypeError(kPromiseExecutorAlreadyInvoked);
    result.resolve = resolve;
    result.reject = reject;
  });

  if (!IS_CALLABLE(result.resolve) || !IS_CALLABLE(result.reject))
      throw MakeTypeError(kPromiseNonCallable);

  return result;
}
function NewPromiseCapability(C) {
  if (C === GlobalPromise) {
    // Optimized case, avoid extra closure.
    var promise = PromiseInit(new GlobalPromise(promiseRawSymbol));
    var callbacks = CreateResolvingFunctions(promise);
    return {
      promise: promise,
      resolve: callbacks.resolve,
      reject: callbacks.reject
    };
  }

  var result = {promise: UNDEFINED, resolve: UNDEFINED, reject: UNDEFINED };
  result.promise = new C((resolve, reject) => {
    if (!IS_UNDEFINED(result.resolve) || !IS_UNDEFINED(result.reject))
        throw MakeTypeError(kPromiseExecutorAlreadyInvoked);
    result.resolve = resolve;
    result.reject = reject;
  });

  if (!IS_CALLABLE(result.resolve) || !IS_CALLABLE(result.reject))
      throw MakeTypeError(kPromiseNonCallable);

  return result;
}
ES#sec-newpromisecapability NewPromiseCapability ( C )