napi: cache Symbol.hasInstance (nodejs#209)

Fixes nodejs#209

src/node_api.cc

@@ -26,9 +26,11 @@ class napi_env__ {
   explicit napi_env__(v8::Isolate* _isolate): isolate(_isolate), last_error() {}
   ~napi_env__() {
     last_exception.Reset();
+    has_instance.Reset();
   }
   v8::Isolate* isolate;
   v8::Persistent<v8::Value> last_exception;
+  v8::Persistent<v8::Value> has_instance;
   napi_extended_error_info last_error;
 };
 
@@ -2120,41 +2122,59 @@ napi_status napi_instanceof(napi_env env,
     return napi_set_last_error(env, napi_function_expected);
   }
 
-  napi_value value, js_result;
+  napi_value value, js_result, has_instance = nullptr;
   napi_status status;
   napi_valuetype value_type;
 
-  // Get "Symbol" from the global object
-  status = napi_get_global(env, &value);
-  if (status != napi_ok) return status;
-  status = napi_get_named_property(env, value, "Symbol", &value);
-  if (status != napi_ok) return status;
-  status = napi_typeof(env, value, &value_type);
-  if (status != napi_ok) return status;
-
-  // Get "hasInstance" from Symbol
-  if (value_type == napi_function) {
-    status = napi_get_named_property(env, value, "hasInstance", &value);
+  fprintf(stderr, "Checking env->has_instance\n");
+
+  if (env->has_instance.IsEmpty()) {
+
+  fprintf(stderr, "env->has_instance is empty\n");
+
+    // Get "Symbol" from the global object
+    status = napi_get_global(env, &value);
+    if (status != napi_ok) return status;
+    status = napi_get_named_property(env, value, "Symbol", &value);
     if (status != napi_ok) return status;
     status = napi_typeof(env, value, &value_type);
     if (status != napi_ok) return status;
 
-    // Retrieve the function at the Symbol(hasInstance) key of the constructor
-    if (value_type == napi_symbol) {
-      status = napi_get_property(env, constructor, value, &value);
+    // Get "hasInstance" from Symbol
+    if (value_type == napi_function) {
+      status = napi_get_named_property(env, value, "hasInstance", &value);
       if (status != napi_ok) return status;
       status = napi_typeof(env, value, &value_type);
       if (status != napi_ok) return status;
 
-      // Call the function to determine whether the object is an instance of the
-      // constructor
-      if (value_type == napi_function) {
-        status = napi_call_function(env, constructor, value, 1, &object,
-          &js_result);
-        if (status != napi_ok) return status;
-        return napi_get_value_bool(env, js_result, result);
+      // If Symbol.hasInstance is of type symbol we've found it
+      if (value_type == napi_symbol) {
+        has_instance = value;
+        env->has_instance.Reset(env->isolate,
+            v8impl::V8LocalValueFromJsValue(value));
       }
     }
+  } else {
+    fprintf(stderr, "env->has_instance is not empty\n");
+    has_instance = v8impl::JsValueFromV8LocalValue(
+        v8::Local<v8::Value>::New(env->isolate, env->has_instance));
+    fprintf(stderr, "env->has_instance assigned from cache\n");
+  }
+
+  if (has_instance) {
+    status = napi_get_property(env, constructor, value, &value);
+    if (status != napi_ok) return status;
+    status = napi_typeof(env, value, &value_type);
+    if (status != napi_ok) return status;
+
+    // Call the function to determine whether the object is an instance of the
+    // constructor
+    if (value_type == napi_function) {
+      status = napi_call_function(env, constructor, value, 1, &object,
+        &js_result);
+      if (status != napi_ok) return status;
+      return napi_get_value_bool(env, js_result, result);
+    }
   }
 
   // If running constructor[Symbol.hasInstance](object) did not work, we perform