Allow JavaScript accessors on API objects.

test/cctest/test-api-accessors.cc

+// Copyright 2015 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.
+
+// TODO(jochen): Remove this after the setting is turned on globally.
+#define V8_IMMINENT_DEPRECATION_WARNINGS
+
+#include "test/cctest/cctest.h"
+
+#include "include/v8.h"
+
+
+#ifdef V8_JS_ACCESSORS
+static void CppAccessor(const v8::FunctionCallbackInfo<v8::Value>& info) {
+  info.GetReturnValue().Set(42);
+}
+
+static const char* JsAccessor =
+    "function firstChildJS(value) { return 41; }; firstChildJS";
+
+TEST(JavascriptAccessors) {
+  v8::Isolate* isolate = CcTest::isolate();
+  v8::HandleScope scope(isolate);
+  LocalContext env;
+
+  // We emulate Embedder-created DOM Node instances. Specifically:
+  // - 'parent': FunctionTemplate ~= DOM Node superclass
+  // - 'child':  FunctionTemplate ~= a specific DOM node type, like a <div />
+  //
+  // We'll install both a C++-based and a JS-based accessor on the parent,
+  // and expect it to be callable on the child.
+
+  // Setup the parent template ( =~ DOM Node w/ accessors).
+  v8::Local<v8::FunctionTemplate> parent = v8::FunctionTemplate::New(isolate);
+  {
+    auto signature = v8::Signature::New(isolate, parent);
+
+    // cpp accessor as "firstChild":
+    parent->PrototypeTemplate()->SetAccessorProperty(
+        v8_str("firstChild"),
+        v8::FunctionTemplate::New(isolate, CppAccessor, v8::Local<v8::Value>(),
+                                  signature));
+
+    // JS accessor as "firstChildJS":
+    auto js_accessor = v8::Local<v8::Function>::Cast(CompileRun(JsAccessor));
+    parent->PrototypeTemplate()->SetAccessorProperty(v8_str("firstChildJS"),
+                                                     js_accessor);
+  }
+
+  // Setup child object ( =~ a specific DOM Node, e.g. a <div> ).
+  // Also, make a creation function on the global object, so we can access it
+  // in a test.
+  v8::Local<v8::FunctionTemplate> child = v8::FunctionTemplate::New(isolate);
+  child->Inherit(parent);
+  CHECK(env->Global()
+            ->Set(env.local(), v8_str("Node"),
+                  child->GetFunction(env.local()).ToLocalChecked())
+            .IsJust());
+
+  // Setup done: Let's test it:
+
+  // The simple case: Run it once.
+  ExpectInt32("var n = new Node(); n.firstChild", 42);
+  ExpectInt32("var n = new Node(); n.firstChildJS", 41);
+
+  // Run them in a loop. This will likely trigger the optimizing compiler:
+  ExpectInt32(
+      "var m = new Node(); "
+      "var sum = 0; "
+      "for (var i = 0; i < 3; ++i) { "
+      "  sum += m.firstChild; "
+      "  sum += m.firstChildJS; "
+      "}; "
+      "sum;",
+      3 * (42 + 41));
+
+  // Obtain the accessor and call it via apply on the Node:
+  ExpectInt32(
+      "var n = new Node(); "
+      "var g = Object.getOwnPropertyDescriptor("
+      "    n.__proto__.__proto__, 'firstChild')['get']; "
+      "g.apply(n);",
+      42);
+  ExpectInt32(
+      "var n = new Node(); "
+      "var g = Object.getOwnPropertyDescriptor("
+      "    n.__proto__.__proto__, 'firstChildJS')['get']; "
+      "g.apply(n);",
+      41);
+
+  // TODO(vogelheim): Verify compatible receiver check works.
+}
+#endif  // V8_JS_ACCESSORS