ladybird/Libraries/LibJS/Runtime/ModuleNamespaceObject.h
Aliaksandr Kalenik 451c947c3f LibJS: Fast-path own-property enumeration and reduce descriptor lookups
Before this change, PropertyNameIterator (used by for..in) and
`Object::enumerable_own_property_names()` (used by `Object.keys()`,
`Object.values()`, and `Object.entries()`) enumerated an object's own
enumerable properties exactly as the spec prescribes:
- Call `internal_own_property_keys()`, allocating a list of JS::Value
  keys.
- For each key, call internal_get_own_property() to obtain a
  descriptor and check `[[Enumerable]]`.

While that is required in the general case (e.g. for Proxy objects or
platform/exotic objects that override `[[OwnPropertyKeys]]`), it's
overkill for ordinary JS objects that store their own properties in the
shape table and indexed-properties storage.

This change introduces `for_each_own_property_with_enumerability()`,
which, for objects where
`eligible_for_own_property_enumeration_fast_path()` is `true`, lets us
read the enumerability directly from shape metadata (and from
indexed-properties storage) without a per-property descriptor lookup.
When we cannot avoid `internal_get_own_property()`, we still
benefit by skipping the temporary `Vector<Value>` of keys and avoiding
the unnecessary round-trip between PropertyKey and Value.
2025-09-21 15:06:32 +02:00

46 lines
2.1 KiB
C++

/*
* Copyright (c) 2022, David Tuin <davidot@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <LibJS/Module.h>
#include <LibJS/Runtime/Completion.h>
#include <LibJS/Runtime/Object.h>
namespace JS {
class ModuleNamespaceObject final : public Object {
JS_OBJECT(ModuleNamespaceObject, Object);
GC_DECLARE_ALLOCATOR(ModuleNamespaceObject);
public:
// 10.4.6 Module Namespace Exotic Objects, https://tc39.es/ecma262/#sec-module-namespace-exotic-objects
virtual ThrowCompletionOr<Object*> internal_get_prototype_of() const override;
virtual ThrowCompletionOr<bool> internal_set_prototype_of(Object* prototype) override;
virtual ThrowCompletionOr<bool> internal_is_extensible() const override;
virtual ThrowCompletionOr<bool> internal_prevent_extensions() override;
virtual ThrowCompletionOr<Optional<PropertyDescriptor>> internal_get_own_property(PropertyKey const&) const override;
virtual ThrowCompletionOr<bool> internal_define_own_property(PropertyKey const&, PropertyDescriptor&, Optional<PropertyDescriptor>* precomputed_get_own_property = nullptr) override;
virtual ThrowCompletionOr<bool> internal_has_property(PropertyKey const&) const override;
virtual ThrowCompletionOr<Value> internal_get(PropertyKey const&, Value receiver, CacheableGetPropertyMetadata* = nullptr, PropertyLookupPhase = PropertyLookupPhase::OwnProperty) const override;
virtual ThrowCompletionOr<bool> internal_set(PropertyKey const&, Value value, Value receiver, CacheableSetPropertyMetadata*, PropertyLookupPhase) override;
virtual ThrowCompletionOr<bool> internal_delete(PropertyKey const&) override;
virtual ThrowCompletionOr<GC::RootVector<Value>> internal_own_property_keys() const override;
virtual void initialize(Realm&) override;
virtual bool eligible_for_own_property_enumeration_fast_path() const final { return false; }
private:
ModuleNamespaceObject(Realm&, Module* module, Vector<Utf16FlyString> exports);
virtual void visit_edges(Visitor&) override;
GC::Ptr<Module> m_module; // [[Module]]
Vector<Utf16FlyString> m_exports; // [[Exports]]
};
}