src: update napi_get_new_target to match docs

The implementation for `napi_get_new_target` needs to return nullptr
when the function is not being called as a constructor.

PR-URL: #490
Reviewed-By: Taylor Woll <tawoll@ntdev.microsoft.com>
Reviewed-By: Jimmy Thomson <jithomso@microsoft.com>

src/node_api_jsrt.cc

@@ -89,9 +89,10 @@ static void napi_clear_last_error();
 struct CallbackInfo {
   napi_value newTarget;
   napi_value thisArg;
-  uint16_t argc;
   napi_value* argv;
   void* data;
+  uint16_t argc;
+  bool isConstructCall;
 };
 
 struct napi_env__ {
@@ -240,6 +241,7 @@ class ExternalCallback {
     CallbackInfo cbInfo;
     cbInfo.thisArg = reinterpret_cast<napi_value>(info->thisArg);
     cbInfo.newTarget = reinterpret_cast<napi_value>(info->newTargetArg);
+    cbInfo.isConstructCall = info->isConstructCall;
     cbInfo.argc = argumentCount - 1;
     cbInfo.argv = reinterpret_cast<napi_value*>(arguments + 1);
     cbInfo.data = externalCallback->_data;
@@ -1385,8 +1387,14 @@ napi_status napi_get_new_target(napi_env env,
                                 napi_value* result) {
   CHECK_ARG(cbinfo);
   CHECK_ARG(result);
+
   const CallbackInfo *info = reinterpret_cast<CallbackInfo*>(cbinfo);
-  *result = info->newTarget;
+  if (info->isConstructCall) {
+    *result = info->newTarget;
+  } else {
+    *result = nullptr;
+  }
+
   return napi_ok;
 }
 

test/addons-napi/test_new_target/binding.c

@@ -15,6 +15,7 @@ napi_value BaseClass(napi_env env, napi_callback_info info) {
   NAPI_ASSERT(env, !result, "this !== new.target");
 
   // new.target !== undefined because we should be called as a new expression
+  NAPI_ASSERT(env, newTargetArg != NULL, "newTargetArg != NULL");
   NAPI_CALL(env, napi_strict_equals(env, newTargetArg, undefined, &result));
   NAPI_ASSERT(env, !result, "new.target !== undefined");
 
@@ -33,6 +34,7 @@ napi_value Constructor(napi_env env, napi_callback_info info) {
   NAPI_CALL(env, napi_get_undefined(env, &undefined));
 
   // new.target !== undefined because we should be called as a new expression
+  NAPI_ASSERT(env, newTargetArg != NULL, "newTargetArg != NULL");
   NAPI_CALL(env, napi_strict_equals(env, newTargetArg, undefined, &result));
   NAPI_ASSERT(env, !result, "new.target !== undefined");
 
@@ -44,15 +46,10 @@ napi_value Constructor(napi_env env, napi_callback_info info) {
 }
 
 napi_value OrdinaryFunction(napi_env env, napi_callback_info info) {
-  bool result;
   napi_value newTargetArg;
   NAPI_CALL(env, napi_get_new_target(env, info, &newTargetArg));
-  napi_value undefined;
-  NAPI_CALL(env, napi_get_undefined(env, &undefined));
 
-  // new.target === undefined because we are not called as a new expression
-  NAPI_CALL(env, napi_strict_equals(env, newTargetArg, undefined, &result));
-  NAPI_ASSERT(env, result, "new.target === undefined");
+  NAPI_ASSERT(env, newTargetArg == NULL, "newTargetArg == NULL");
 
   napi_value _true;
   NAPI_CALL(env, napi_get_boolean(env, true, &_true));