[v8-users] Intercepting the setting of static and instance methods

[Darin Dimitrov]

I am embedding V8 in my application and registered a custom class 
(MyClass). I am looking for a way to intercept the setting of methods on 
this class.

Here's my code:

    
auto platform = platform::NewDefaultPlatform();
V8::InitializePlatform(platform.get());
V8::Initialize();
std::string flags = "--expose_gc --jitless";
V8::SetFlagsFromString(flags.c_str(), flags.size());
Isolate::CreateParams create_params;
create_params.array_buffer_allocator = ArrayBuffer::Allocator::
NewDefaultAllocator();

Isolate* isolate = Isolate::New(create_params);
{
    Isolate::Scope isolate_scope(isolate);
    HandleScope handle_scope(isolate);

    Local<FunctionTemplate> myClassTemplate = FunctionTemplate::New(isolate
);
    Local<FunctionTemplate> myInstanceMethodTemplate = FunctionTemplate::New
(isolate);
    myClassTemplate->InstanceTemplate()->Set(v8::String::NewFromUtf8(isolate
, "myInstanceMethod", v8::NewStringType::kNormal).ToLocalChecked(), 
myInstanceMethodTemplate);

    Local<ObjectTemplate> globalTemplate = ObjectTemplate::New(isolate);
    globalTemplate->Set(v8::String::NewFromUtf8(isolate, "MyClass", v8::
NewStringType::kNormal).ToLocalChecked(), myClassTemplate);

    Local<v8::Context> context = v8::Context::New(isolate, nullptr, 
globalTemplate);
    Context::Scope context_scope(context);
    {
        Local<v8::Function> myClassCtor = myClassTemplate->GetFunction(
context).ToLocalChecked();
        Local<v8::Function> myStaticMethod = v8::Function::New(context, 
nullptr).ToLocalChecked();
        assert(myClassCtor->Set(context, v8::String::NewFromUtf8(isolate, 
"myStaticMethod", v8::NewStringType::kNormal).ToLocalChecked(), 
myStaticMethod).FromMaybe(false));

        std::string src = R"(
           // I want to intercept setting this static method and raise some 
C++ callback when this code is executed
           MyClass.myStaticMethod = () => { };

           // I want to intercept setting this instance method and raise 
some C++ callback when this code is executed
           MyClass.prototype.myInstanceMethod = () => { };
       )";

       Local<v8::String> source = v8::String::NewFromUtf8(isolate, src.c_str
(), v8::NewStringType::kNormal).ToLocalChecked();
       Local<Script> script = Script::Compile(context, source).
ToLocalChecked();
       Local<Value> result = script->Run(context).ToLocalChecked();
       assert(!result.IsEmpty());
   }

}

isolate->Dispose();
V8::Dispose();
V8::ShutdownPlatform();
delete create_params.array_buffer_allocator;



In this code I need a C++ callback to be raised when the script is trying 
to replace some existing static or instance method on my custom class.

Is there some API in V8 that I can use to achieve that?

I have tried registering a NamedPropertyHandlerConfiguration but my 
callback is never called:

myClassTemplate->InstanceTemplate()->SetHandler(
NamedPropertyHandlerConfiguration(nullptr, [](Local<Name> property, Local<
Value> value, const PropertyCallbackInfo<Value>& info) {
    printf("ok");
}));


Basically I need a way to detect that some script is trying to replace the 
methods which I have registered manually.

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