implementing-jsc-classes-cpp

Verwendung

Installationsbefehl kopieren und das Quellpaket vor der Installation in der eigenen Agentenumgebung prüfen.
Benötigte Werkzeuge, Zugangsdaten und Hosts im Original prüfen.
Eingabe und gewünschtes Ergebnis beschreiben und die Ausgabe mit den Quellen abgleichen.

npx skills add https://github.com/oven-sh/bun --skill implementing-jsc-classes-cpp

Vor dem Start

Die Installation umfasst weder Modellabo noch API-Kontingent oder Dateizugriffsrechte.
Sterne und Installationen zeigen Aktivität, keine unabhängige Qualitäts- oder Sicherheitsprüfung.

Originales Skill-Dokument

Aus dem Quell-Repository gerendert; Überschriften, Beispiele, Code, Tabellen, Links und Bilder bleiben erhalten.

Implementing JavaScript Classes in C++

Class Structure

For publicly accessible Constructor and Prototype, create 3 classes:

`class Foo : public JSC::DestructibleObject` - if C++ fields exist; otherwise use JSC::constructEmptyObject with putDirectOffset
`class FooPrototype : public JSC::JSNonFinalObject`
`class FooConstructor : public JSC::InternalFunction`

No public constructor? Only Prototype and class needed.

Iso Subspaces

Classes with C++ fields need subspaces in:

src/jsc/bindings/webcore/DOMClientIsoSubspaces.h
src/jsc/bindings/webcore/DOMIsoSubspaces.h

cpp

template<typename MyClassT, JSC::SubspaceAccess mode>
static JSC::GCClient::IsoSubspace* subspaceFor(JSC::VM& vm) {
    if constexpr (mode == JSC::SubspaceAccess::Concurrently)
        return nullptr;
    return WebCore::subspaceForImpl<MyClassT, WebCore::UseCustomHeapCellType::No>(
        vm, BUN_SUBSPACE_SLOTS(m_clientSubspaceForMyClassT, m_subspaceForMyClassT));
}

subspaceForImpl only reads the slots inline. The subspaces themselves are created by subspaceForImplSlow in src/jsc/bindings/BunClientData.cpp, which is the only place that constructs an IsoSubspace (test/internal/source-lints/iso-subspace-creation.test.ts checks this).

Property Definitions

cpp

static JSC_DECLARE_HOST_FUNCTION(jsFooProtoFuncMethod);
static JSC_DECLARE_CUSTOM_GETTER(jsFooGetter_property);

static const HashTableValue JSFooPrototypeTableValues[] = {
    { "property"_s, static_cast<unsigned>(PropertyAttribute::ReadOnly | PropertyAttribute::CustomAccessor), NoIntrinsic, { HashTableValue::GetterSetterType, jsFooGetter_property, 0 } },
    { "method"_s, static_cast<unsigned>(PropertyAttribute::Function), NoIntrinsic, { HashTableValue::NativeFunctionType, jsFooProtoFuncMethod, 1 } },
};

Prototype Class

cpp

class JSFooPrototype final : public JSC::JSNonFinalObject {
public:
    using Base = JSC::JSNonFinalObject;
    static constexpr unsigned StructureFlags = Base::StructureFlags;

    static JSFooPrototype* create(JSC::VM& vm, JSC::JSGlobalObject* globalObject, JSC::Structure* structure) {
        JSFooPrototype* prototype = new (NotNull, allocateCell<JSFooPrototype>(vm)) JSFooPrototype(vm, structure);
        prototype->finishCreation(vm);
        return prototype;
    }

    template<typename, JSC::SubspaceAccess>
    static JSC::GCClient::IsoSubspace* subspaceFor(JSC::VM& vm) { return &vm.plainObjectSpace(); }

    DECLARE_INFO;

    static JSC::Structure* createStructure(JSC::VM& vm, JSC::JSGlobalObject* globalObject, JSC::JSValue prototype) {
        auto* structure = JSC::Structure::create(vm, globalObject, prototype, JSC::TypeInfo(JSC::ObjectType, StructureFlags), info());
        structure->setMayBePrototype(true);
        return structure;
    }

private:
    JSFooPrototype(JSC::VM& vm, JSC::Structure* structure) : Base(vm, structure) {}
    void finishCreation(JSC::VM& vm);
};

void JSFooPrototype::finishCreation(VM& vm) {
    Base::finishCreation(vm);
    reifyStaticProperties(vm, JSFoo::info(), JSFooPrototypeTableValues, *this);
    JSC_TO_STRING_TAG_WITHOUT_TRANSITION();
}

Getter/Setter/Function Definitions

cpp

// Getter
JSC_DEFINE_CUSTOM_GETTER(jsFooGetter_prop, (JSGlobalObject* globalObject, EncodedJSValue thisValue, PropertyName)) {
    VM& vm = globalObject->vm();
    auto scope = DECLARE_THROW_SCOPE(vm);
    JSFoo* thisObject = jsDynamicCast<JSFoo*>(JSValue::decode(thisValue));
    if (UNLIKELY(!thisObject)) {
        Bun::throwThisTypeError(*globalObject, scope, "JSFoo"_s, "prop"_s);
        return {};
    }
    return JSValue::encode(jsBoolean(thisObject->value()));
}

// Function
JSC_DEFINE_HOST_FUNCTION(jsFooProtoFuncMethod, (JSGlobalObject* globalObject, CallFrame* callFrame)) {
    VM& vm = globalObject->vm();
    auto scope = DECLARE_THROW_SCOPE(vm);
    auto* thisObject = jsDynamicCast<JSFoo*>(callFrame->thisValue());
    if (UNLIKELY(!thisObject)) {
        Bun::throwThisTypeError(*globalObject, scope, "Foo"_s, "method"_s);
        return {};
    }
    return JSValue::encode(thisObject->doSomething(vm, globalObject));
}

Constructor Class

cpp

class JSFooConstructor final : public JSC::InternalFunction {
public:
    using Base = JSC::InternalFunction;
    static constexpr unsigned StructureFlags = Base::StructureFlags;

    static JSFooConstructor* create(JSC::VM& vm, JSC::Structure* structure, JSC::JSObject* prototype) {
        JSFooConstructor* constructor = new (NotNull, JSC::allocateCell<JSFooConstructor>(vm)) JSFooConstructor(vm, structure);
        constructor->finishCreation(vm, prototype);
        return constructor;
    }

    DECLARE_INFO;

    template<typename CellType, JSC::SubspaceAccess>
    static JSC::GCClient::IsoSubspace* subspaceFor(JSC::VM& vm) { return &vm.internalFunctionSpace(); }

    static JSC::Structure* createStructure(JSC::VM& vm, JSC::JSGlobalObject* globalObject, JSC::JSValue prototype) {
        return JSC::Structure::create(vm, globalObject, prototype, JSC::TypeInfo(JSC::InternalFunctionType, StructureFlags), info());
    }

private:
    JSFooConstructor(JSC::VM& vm, JSC::Structure* structure) : Base(vm, structure, callFoo, constructFoo) {}

    void finishCreation(JSC::VM& vm, JSC::JSObject* prototype) {
        Base::finishCreation(vm, 0, "Foo"_s);
        putDirectWithoutTransition(vm, vm.propertyNames->prototype, prototype, JSC::PropertyAttribute::DontEnum | JSC::PropertyAttribute::DontDelete | JSC::PropertyAttribute::ReadOnly);
    }
};

Structure Caching

Add to ZigGlobalObject.h:

cpp

JSC::LazyClassStructure m_JSFooClassStructure;

Initialize in ZigGlobalObject.cpp:

cpp

m_JSFooClassStructure.initLater([](LazyClassStructure::Initializer& init) {
    Bun::initJSFooClassStructure(init);
});

Visit in visitChildrenImpl:

cpp

m_JSFooClassStructure.visit(visitor);

Expose to Zig

cpp

extern "C" JSC::EncodedJSValue Bun__JSFooConstructor(Zig::GlobalObject* globalObject) {
    return JSValue::encode(globalObject->m_JSFooClassStructure.constructor(globalObject));
}

extern "C" EncodedJSValue Bun__Foo__toJS(Zig::GlobalObject* globalObject, Foo* foo) {
    auto* structure = globalObject->m_JSFooClassStructure.get(globalObject);
    return JSValue::encode(JSFoo::create(globalObject->vm(), structure, globalObject, WTFMove(foo)));
}

Include #include "root.h" at the top of C++ files.