In addition to what Simon said: from a V8 API point of view, we have a
strict type system and class hierarchy (this is C++ after all, not
JavaScript). A v8::Name is a name, not a function. For a v8::Local<v8::Name>
key, it will and must always be the case that key->IsName() returns true,
and key->IsFunction() returns false. Anything else would be a very serious
bug.
On Thu, Sep 26, 2019 at 8:44 AM 'Simon Zünd' via v8-users <
v8-users@googlegroups.com> wrote:
> In terms of the JavaScript spec, you are performing a [[Set]] operation
> with `dict[x] = x`. The key for [[Set]] must be a valid property key, which
> is either a String or a Symbol. In this case, the code actually looks more
> like `dict[x.toString()] = x`. This is just how JavaScript works, and is
> intended.
>
> On Thu, Sep 26, 2019 at 8:07 AM Gautham B A <gautham.bangal...@gmail.com>
> wrote:
>
>> Hi all,
>>
>> Calling IsFunction() on v8::Local<v8::Name> is returning false, even
>> though v8::Local<v8::Name> was pointing to a function in JavaScript. Is
>> this expected? Consider the following code -
>>
>> #include <iostream>
>> #include <libplatform/libplatform.h>
>> #include <ostream>
>> #include <v8.h>
>>
>>
>> void Getter(v8::Local<v8::Name> key,
>> const v8::PropertyCallbackInfo<v8::Value> &info) {
>> std::cout << "Getter:" << std::endl;
>> std::cout << "IsFunction: " << key->IsFunction() << std::endl;
>> }
>>
>>
>> void Setter(v8::Local<v8::Name> key, v8::Local<v8::Value> value,
>> const v8::PropertyCallbackInfo<v8::Value> &info) {
>> std::cout << "Setter:" << std::endl;
>> // key->IsFunction() returns false, expected to be true
>> std::cout << "Key IsFunction: " << key->IsFunction() << std::endl;
>>
>>
>> // value->IsFunction() returns true, as expected
>> std::cout << "\nValue IsFunction:" << value->IsFunction() << std::endl;
>> }
>>
>>
>> void Deleter(v8::Local<v8::Name> key,
>> const v8::PropertyCallbackInfo<v8::Boolean> &info) {}
>>
>>
>> bool InstallMap(v8::Isolate *isolate, const v8::Local<v8::Context> &
>> context) {
>> v8::HandleScope handle_scope(isolate);
>> auto obj_template = v8::ObjectTemplate::New(isolate);
>> obj_template->SetHandler(
>> v8::NamedPropertyHandlerConfiguration(Getter, Setter, nullptr,
>> Deleter));
>>
>>
>> v8::Local<v8::Object> obj;
>> if (!obj_template->NewInstance(context).ToLocal(&obj)) {
>> std::cerr << "Unable to instantiate object template" << std::endl;
>> return false;
>> }
>>
>>
>> v8::Local<v8::String> obj_name;
>> if (!v8::String::NewFromUtf8(isolate, "dict", v8::String::kNormalString
>> )
>> ->ToString(context)
>> .ToLocal(&obj_name)) {
>> std::cerr << "Unable to create map key name" << std::endl;
>> return false;
>> }
>>
>>
>> auto global = context->Global();
>> if (!global->Set(context, obj_name, obj).FromJust()) {
>> std::cerr << "Unable to install object into global scope" << std::
>> endl;
>> return false;
>> }
>> return true;
>> }
>>
>>
>> int main(int argc, char *argv[]) {
>> const auto script_str = R"(
>> function x() {
>> }
>>
>>
>> dict[x] = x;
>> )";
>>
>>
>> v8::V8::InitializeICUDefaultLocation(argv[0]);
>> v8::V8::InitializeExternalStartupData(argv[0]);
>> auto platform = v8::platform::NewDefaultPlatform();
>> v8::V8::InitializePlatform(platform.get());
>> v8::V8::Initialize();
>>
>>
>> v8::Isolate::CreateParams create_params;
>> create_params.array_buffer_allocator =
>> v8::ArrayBuffer::Allocator::NewDefaultAllocator();
>> v8::Isolate *isolate = v8::Isolate::New(create_params);
>> {
>> v8::Isolate::Scope isolate_scope(isolate);
>> v8::HandleScope handle_scope(isolate);
>> auto context = v8::Context::New(isolate);
>> v8::Context::Scope context_scope(context);
>>
>>
>> InstallMap(isolate, context);
>>
>>
>> auto source =
>> v8::String::NewFromUtf8(isolate, script_str, v8::NewStringType::
>> kNormal)
>> .ToLocalChecked();
>> auto script = v8::Script::Compile(context, source).ToLocalChecked();
>> auto result = script->Run(context).ToLocalChecked();
>> v8::String::Utf8Value result_utf8(isolate, result);
>> std::cout << *result_utf8 << std::endl;
>> }
>> isolate->Dispose();
>> v8::V8::Dispose();
>> v8::V8::ShutdownPlatform();
>> delete create_params.array_buffer_allocator;
>> return 0;
>> }
>>
>>
>> As seen in the code above, I'm exposing a global variable dict which has
>> the Setter, Getter and Deleter callbacks set appropriately on dict.
>>
>> function x() {
>> }
>> dict[x] = x;
>> When I run the above JavaScript code, The Setter callback gets called and
>> I see that *name* and *value* have different results upon calling
>> IsFunction() on them.
>> Could someone please tell me if this is the expected behavior, if so, the
>> reason behind why it is so?
>>
>> Thanks,
>> --Gautham
>>
>> --
>
>
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