Mirror API for IsAsyncFunction

src/runtime/runtime-function.cc

Index: src/runtime/runtime-function.cc
diff --git a/src/runtime/runtime-function.cc b/src/runtime/runtime-function.cc
index fa509419257045d15fa83af562258cd30182fc1f..be958764a4566772dbf5e3f3e241fc60d6885cf5 100644
--- a/src/runtime/runtime-function.cc
+++ b/src/runtime/runtime-function.cc
@@ -292,5 +292,16 @@ RUNTIME_FUNCTION(Runtime_FunctionToString) {
              : *JSFunction::ToString(Handle<JSFunction>::cast(function));
 }
 
+RUNTIME_FUNCTION(Runtime_FunctionIsAsyncFunction) {
+  SealHandleScope shs(isolate);
+  DCHECK_EQ(1, args.length());
+  CONVERT_ARG_HANDLE_CHECKED(JSReceiver, function, 0);
+  bool is_async = false;
+  if (function->IsFunction()) {
+    is_async = Handle<JSFunction>::cast(function)->shared()->is_async();
+  }
+  return isolate->heap()->ToBoolean(is_async);
+}
+
 }  // namespace internal
 }  // namespace v8