Use the instance type to determine if an object is a promise.

src/api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 3019 matching lines @@
 
 bool Value::IsMapIterator() const {
   return Utils::OpenHandle(this)->IsJSMapIterator();
 }
 
 
 bool Value::IsSetIterator() const {
   return Utils::OpenHandle(this)->IsJSSetIterator();
 }
 
-
-bool Value::IsPromise() const {
-  auto self = Utils::OpenHandle(this);
-  return i::Object::IsPromise(self);
-}
-
+bool Value::IsPromise() const { return Utils::OpenHandle(this)->IsJSPromise(); }
 
 MaybeLocal<String> Value::ToString(Local<Context> context) const {
   auto obj = Utils::OpenHandle(this);
   if (obj->IsString()) return ToApiHandle<String>(obj);
   PREPARE_FOR_EXECUTION(context, Object, ToString, String);
   Local<String> result;
   has_pending_exception =
       !ToLocal<String>(i::Object::ToString(isolate, obj), &result);
   RETURN_ON_FAILED_EXECUTION(String);
   RETURN_ESCAPED(result);
@@ skipping 5814 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8