ladybird/Userland/Libraries/LibJS/Runtime/Object.cpp

/*
 * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
 * Copyright (c) 2020-2021, Linus Groh <linusg@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Debug.h>
#include <AK/String.h>
#include <AK/TemporaryChange.h>
#include <LibJS/Heap/Heap.h>
#include <LibJS/Interpreter.h>
#include <LibJS/Runtime/Accessor.h>
#include <LibJS/Runtime/Array.h>
#include <LibJS/Runtime/Error.h>
#include <LibJS/Runtime/GlobalObject.h>
#include <LibJS/Runtime/NativeFunction.h>
#include <LibJS/Runtime/NativeProperty.h>
#include <LibJS/Runtime/Object.h>
#include <LibJS/Runtime/ProxyObject.h>
#include <LibJS/Runtime/Shape.h>
#include <LibJS/Runtime/StringObject.h>
#include <LibJS/Runtime/TemporaryClearException.h>
#include <LibJS/Runtime/Value.h>

namespace JS {

PropertyDescriptor PropertyDescriptor::from_dictionary(VM& vm, const Object& object)
{
    PropertyAttributes attributes;
    if (object.has_property(vm.names.configurable)) {
        attributes.set_has_configurable();
        if (object.get(vm.names.configurable).value_or(Value(false)).to_boolean())
            attributes.set_configurable();
        if (vm.exception())
            return {};
    }
    if (object.has_property(vm.names.enumerable)) {
        attributes.set_has_enumerable();
        if (object.get(vm.names.enumerable).value_or(Value(false)).to_boolean())
            attributes.set_enumerable();
        if (vm.exception())
            return {};
    }
    if (object.has_property(vm.names.writable)) {
        attributes.set_has_writable();
        if (object.get(vm.names.writable).value_or(Value(false)).to_boolean())
            attributes.set_writable();
        if (vm.exception())
            return {};
    }
    PropertyDescriptor descriptor { attributes, object.get(vm.names.value), nullptr, nullptr };
    if (vm.exception())
        return {};
    auto getter = object.get(vm.names.get);
    if (vm.exception())
        return {};
    if (getter.is_function())
        descriptor.getter = &getter.as_function();
    auto setter = object.get(vm.names.set);
    if (vm.exception())
        return {};
    if (setter.is_function())
        descriptor.setter = &setter.as_function();
    return descriptor;
}

// 10.1.12 OrdinaryObjectCreate ( proto [ , additionalInternalSlotsList ] ), https://tc39.es/ecma262/#sec-ordinaryobjectcreate
Object* Object::create(GlobalObject& global_object, Object* prototype)
{
    if (!prototype)
        return global_object.heap().allocate<Object>(global_object, *global_object.empty_object_shape());
    else if (prototype == global_object.object_prototype())
        return global_object.heap().allocate<Object>(global_object, *global_object.new_object_shape());
    else
        return global_object.heap().allocate<Object>(global_object, *prototype);
}

Object::Object(GlobalObjectTag)
{
    // This is the global object
    m_shape = heap().allocate_without_global_object<Shape>(*this);
}

Object::Object(ConstructWithoutPrototypeTag, GlobalObject& global_object)
{
    m_shape = heap().allocate_without_global_object<Shape>(global_object);
}

Object::Object(Object& prototype)
{
    m_shape = prototype.global_object().empty_object_shape();
    set_prototype(&prototype);
}

Object::Object(Shape& shape)
    : m_shape(&shape)
{
    m_storage.resize(shape.property_count());
}

void Object::initialize(GlobalObject&)
{
}

Object::~Object()
{
}

Object* Object::prototype()
{
    return shape().prototype();
}

const Object* Object::prototype() const
{
    return shape().prototype();
}

// 10.1.2.1 OrdinarySetPrototypeOf ( O, V ), https://tc39.es/ecma262/#sec-ordinarysetprototypeof
bool Object::set_prototype(Object* new_prototype)
{
    if (prototype() == new_prototype)
        return true;
    if (!m_is_extensible)
        return false;
    auto* prototype = new_prototype;
    while (prototype) {
        if (prototype == this)
            return false;
        // NOTE: This is a best-effort implementation of the following step:
        // "If p.[[GetPrototypeOf]] is not the ordinary object internal method defined in 10.1.1,
        // set done to true."
        // We don't have a good way of detecting whether certain virtual Object methods have been
        // overridden by a given object, but as ProxyObject is the only one doing that, this check
        // does the trick.
        if (is<ProxyObject>(prototype))
            break;
        prototype = prototype->prototype();
    }
    auto& shape = this->shape();
    if (shape.is_unique())
        shape.set_prototype_without_transition(new_prototype);
    else
        m_shape = shape.create_prototype_transition(new_prototype);
    return true;
}

bool Object::has_prototype(const Object* prototype) const
{
    for (auto* object = this->prototype(); object; object = object->prototype()) {
        if (vm().exception())
            return false;
        if (object == prototype)
            return true;
    }
    return false;
}

bool Object::prevent_extensions()
{
    m_is_extensible = false;
    return true;
}

// 7.3.15 SetIntegrityLevel ( O, level ), https://tc39.es/ecma262/#sec-setintegritylevel
bool Object::set_integrity_level(IntegrityLevel level)
{
    // FIXME: This feels clunky and should get nicer abstractions.
    auto update_property = [this](auto& property_name, auto new_attributes) {
        if (property_name.is_number()) {
            auto value_and_attributes = m_indexed_properties.get(nullptr, property_name.as_number(), false).value();
            auto value = value_and_attributes.value;
            auto attributes = value_and_attributes.attributes.bits() & new_attributes;
            m_indexed_properties.put(nullptr, property_name.as_number(), value, attributes, false);
        } else {
            auto metadata = shape().lookup(property_name.to_string_or_symbol()).value();
            auto attributes = metadata.attributes.bits() & new_attributes;
            if (m_shape->is_unique())
                m_shape->reconfigure_property_in_unique_shape(property_name.to_string_or_symbol(), attributes);
            else
                set_shape(*m_shape->create_configure_transition(property_name.to_string_or_symbol(), attributes));
        }
    };

    auto& vm = this->vm();
    auto status = prevent_extensions();
    if (vm.exception())
        return false;
    if (!status)
        return false;
    auto keys = get_own_properties(PropertyKind::Key);
    if (vm.exception())
        return false;
    switch (level) {
    case IntegrityLevel::Sealed:
        for (auto& key : keys) {
            auto property_name = PropertyName::from_value(global_object(), key);
            if (property_name.is_string() && property_name.string_may_be_number()) {
                i32 property_index = property_name.as_string().to_int().value_or(-1);
                if (property_index >= 0)
                    property_name = property_index;
            }
            update_property(property_name, ~Attribute::Configurable);
            if (vm.exception())
                return {};
        }
        break;
    case IntegrityLevel::Frozen:
        for (auto& key : keys) {
            auto property_name = PropertyName::from_value(global_object(), key);
            if (property_name.is_string() && property_name.string_may_be_number()) {
                i32 property_index = property_name.as_string().to_int().value_or(-1);
                if (property_index >= 0)
                    property_name = property_index;
            }
            auto property_descriptor = get_own_property_descriptor(property_name);
            if (!property_descriptor.has_value())
                continue;
            u8 attributes = property_descriptor->is_accessor_descriptor()
                ? ~Attribute::Configurable
                : ~Attribute::Configurable & ~Attribute::Writable;
            update_property(property_name, attributes);
            if (vm.exception())
                return {};
        }
        break;
    default:
        VERIFY_NOT_REACHED();
    }
    return true;
}

// 7.3.16 TestIntegrityLevel ( O, level ), https://tc39.es/ecma262/#sec-testintegritylevel
bool Object::test_integrity_level(IntegrityLevel level)
{
    auto& vm = this->vm();
    auto extensible = is_extensible();
    if (vm.exception())
        return false;
    if (extensible)
        return false;
    auto keys = get_own_properties(PropertyKind::Key);
    if (vm.exception())
        return false;
    for (auto& key : keys) {
        auto property_name = PropertyName::from_value(global_object(), key);
        auto property_descriptor = get_own_property_descriptor(property_name);
        if (!property_descriptor.has_value())
            continue;
        if (property_descriptor->attributes.is_configurable())
            return false;
        if (level == IntegrityLevel::Frozen && property_descriptor->is_data_descriptor()) {
            if (property_descriptor->attributes.is_writable())
                return false;
        }
    }
    return true;
}

Value Object::get_own_property(const PropertyName& property_name, Value receiver, bool without_side_effects) const
{
    VERIFY(property_name.is_valid());
    VERIFY(!receiver.is_empty());

    Value value_here;

    if (property_name.is_number()) {
        auto existing_property = m_indexed_properties.get(nullptr, property_name.as_number(), false);
        if (!existing_property.has_value())
            return {};
        value_here = existing_property.value().value.value_or(js_undefined());
    } else {
        auto metadata = shape().lookup(property_name.to_string_or_symbol());
        if (!metadata.has_value())
            return {};
        value_here = m_storage[metadata.value().offset].value_or(js_undefined());
    }

    VERIFY(!value_here.is_empty());
    if (!without_side_effects) {
        if (value_here.is_accessor())
            return value_here.as_accessor().call_getter(receiver);
        if (value_here.is_native_property())
            return call_native_property_getter(value_here.as_native_property(), receiver);
    }
    return value_here;
}

MarkedValueList Object::get_own_properties(PropertyKind kind, bool only_enumerable_properties, GetOwnPropertyReturnType return_type) const
{
    MarkedValueList properties(heap());

    // FIXME: Support generic iterables
    if (is<StringObject>(*this)) {
        auto str = static_cast<const StringObject&>(*this).primitive_string().string();

        for (size_t i = 0; i < str.length(); ++i) {
            if (kind == PropertyKind::Key) {
                properties.append(js_string(vm(), String::number(i)));
            } else if (kind == PropertyKind::Value) {
                properties.append(js_string(vm(), String::formatted("{:c}", str[i])));
            } else {
                auto* entry_array = Array::create(global_object());
                entry_array->define_property(0, js_string(vm(), String::number(i)));
                entry_array->define_property(1, js_string(vm(), String::formatted("{:c}", str[i])));
                properties.append(entry_array);
            }
            if (vm().exception())
                return MarkedValueList { heap() };
        }

        return properties;
    }

    if (return_type != GetOwnPropertyReturnType::SymbolOnly) {
        for (auto& entry : m_indexed_properties) {
            auto value_and_attributes = entry.value_and_attributes(const_cast<Object*>(this));
            if (only_enumerable_properties && !value_and_attributes.attributes.is_enumerable())
                continue;

            if (kind == PropertyKind::Key) {
                properties.append(js_string(vm(), String::number(entry.index())));
            } else if (kind == PropertyKind::Value) {
                properties.append(value_and_attributes.value);
            } else {
                auto* entry_array = Array::create(global_object());
                entry_array->define_property(0, js_string(vm(), String::number(entry.index())));
                entry_array->define_property(1, value_and_attributes.value);
                properties.append(entry_array);
            }
            if (vm().exception())
                return MarkedValueList { heap() };
        }
    }

    auto add_property_to_results = [&](auto& property) {
        if (kind == PropertyKind::Key) {
            properties.append(property.key.to_value(vm()));
        } else if (kind == PropertyKind::Value) {
            properties.append(get(property.key));
        } else {
            auto* entry_array = Array::create(global_object());
            entry_array->define_property(0, property.key.to_value(vm()));
            entry_array->define_property(1, get(property.key));
            properties.append(entry_array);
        }
    };

    // NOTE: Most things including for..in/of and Object.{keys,values,entries}() use StringOnly, and in those
    // cases we won't be iterating the ordered property table twice. We can certainly improve this though.
    if (return_type == GetOwnPropertyReturnType::All || return_type == GetOwnPropertyReturnType::StringOnly) {
        for (auto& it : shape().property_table_ordered()) {
            if (only_enumerable_properties && !it.value.attributes.is_enumerable())
                continue;
            if (it.key.is_symbol())
                continue;
            add_property_to_results(it);
            if (vm().exception())
                return MarkedValueList { heap() };
        }
    }
    if (return_type == GetOwnPropertyReturnType::All || return_type == GetOwnPropertyReturnType::SymbolOnly) {
        for (auto& it : shape().property_table_ordered()) {
            if (only_enumerable_properties && !it.value.attributes.is_enumerable())
                continue;
            if (it.key.is_string())
                continue;
            add_property_to_results(it);
            if (vm().exception())
                return MarkedValueList { heap() };
        }
    }

    return properties;
}

// 7.3.23 EnumerableOwnPropertyNames ( O, kind ), https://tc39.es/ecma262/#sec-enumerableownpropertynames
MarkedValueList Object::get_enumerable_own_property_names(PropertyKind kind) const
{
    return get_own_properties(kind, true, Object::GetOwnPropertyReturnType::StringOnly);
}

Optional<PropertyDescriptor> Object::get_own_property_descriptor(const PropertyName& property_name) const
{
    VERIFY(property_name.is_valid());

    Value value;
    PropertyAttributes attributes;

    if (property_name.is_number()) {
        auto existing_value = m_indexed_properties.get(nullptr, property_name.as_number(), false);
        if (!existing_value.has_value())
            return {};
        value = existing_value.value().value;
        attributes = existing_value.value().attributes;
    } else {
        if (property_name.is_string() && property_name.string_may_be_number()) {
            i32 property_index = property_name.as_string().to_int().value_or(-1);
            if (property_index >= 0)
                return get_own_property_descriptor(property_index);
        }
        auto metadata = shape().lookup(property_name.to_string_or_symbol());
        if (!metadata.has_value())
            return {};
        value = m_storage[metadata.value().offset];
        attributes = metadata.value().attributes;
    }

    PropertyDescriptor descriptor { attributes, {}, nullptr, nullptr };
    if (value.is_native_property()) {
        auto result = call_native_property_getter(value.as_native_property(), const_cast<Object*>(this));
        descriptor.value = result.value_or(js_undefined());
    } else if (value.is_accessor()) {
        auto& pair = value.as_accessor();
        if (pair.getter())
            descriptor.getter = pair.getter();
        if (pair.setter())
            descriptor.setter = pair.setter();
    } else {
        descriptor.value = value.value_or(js_undefined());
    }

    return descriptor;
}

// Equivalent to:
// 6.2.5.4 FromPropertyDescriptor ( Desc ), https://tc39.es/ecma262/#sec-frompropertydescriptor
Value Object::get_own_property_descriptor_object(const PropertyName& property_name) const
{
    VERIFY(property_name.is_valid());

    auto& vm = this->vm();
    auto& global_object = this->global_object();

    auto descriptor_opt = get_own_property_descriptor(property_name);
    if (!descriptor_opt.has_value())
        return js_undefined();
    auto descriptor = descriptor_opt.value();

    auto* descriptor_object = Object::create(global_object, global_object.object_prototype());
    if (descriptor.is_data_descriptor()) {
        descriptor_object->define_property(vm.names.value, descriptor.value.value_or(js_undefined()));
        descriptor_object->define_property(vm.names.writable, Value(descriptor.attributes.is_writable()));
    } else {
        VERIFY(descriptor.is_accessor_descriptor());
        descriptor_object->define_property(vm.names.get, descriptor.getter ? Value(descriptor.getter) : js_undefined());
        descriptor_object->define_property(vm.names.set, descriptor.setter ? Value(descriptor.setter) : js_undefined());
    }
    descriptor_object->define_property(vm.names.enumerable, Value(descriptor.attributes.is_enumerable()));
    descriptor_object->define_property(vm.names.configurable, Value(descriptor.attributes.is_configurable()));
    return descriptor_object;
}

void Object::set_shape(Shape& new_shape)
{
    m_storage.resize(new_shape.property_count());
    m_shape = &new_shape;
}

bool Object::define_property(const StringOrSymbol& property_name, const Object& descriptor, bool throw_exceptions)
{
    auto& vm = this->vm();
    bool is_accessor_property = descriptor.has_property(vm.names.get) || descriptor.has_property(vm.names.set);
    PropertyAttributes attributes;
    if (descriptor.has_property(vm.names.configurable)) {
        attributes.set_has_configurable();
        if (descriptor.get(vm.names.configurable).value_or(Value(false)).to_boolean())
            attributes.set_configurable();
        if (vm.exception())
            return false;
    }
    if (descriptor.has_property(vm.names.enumerable)) {
        attributes.set_has_enumerable();
        if (descriptor.get(vm.names.enumerable).value_or(Value(false)).to_boolean())
            attributes.set_enumerable();
        if (vm.exception())
            return false;
    }

    if (is_accessor_property) {
        if (descriptor.has_property(vm.names.value) || descriptor.has_property(vm.names.writable)) {
            if (throw_exceptions)
                vm.throw_exception<TypeError>(global_object(), ErrorType::AccessorValueOrWritable);
            return false;
        }

        auto getter = descriptor.get(vm.names.get).value_or(js_undefined());
        if (vm.exception())
            return {};
        auto setter = descriptor.get(vm.names.set).value_or(js_undefined());
        if (vm.exception())
            return {};

        Function* getter_function { nullptr };
        Function* setter_function { nullptr };

        if (getter.is_function()) {
            getter_function = &getter.as_function();
        } else if (!getter.is_undefined()) {
            vm.throw_exception<TypeError>(global_object(), ErrorType::AccessorBadField, "get");
            return false;
        }

        if (setter.is_function()) {
            setter_function = &setter.as_function();
        } else if (!setter.is_undefined()) {
            vm.throw_exception<TypeError>(global_object(), ErrorType::AccessorBadField, "set");
            return false;
        }

        dbgln_if(OBJECT_DEBUG, "Defining new property {} with accessor descriptor {{ attributes={}, getter={}, setter={} }}", property_name.to_display_string(), attributes, getter, setter);

        return define_property(property_name, Accessor::create(vm, getter_function, setter_function), attributes, throw_exceptions);
    }

    auto value = descriptor.get(vm.names.value);
    if (vm.exception())
        return {};
    if (descriptor.has_property(vm.names.writable)) {
        attributes.set_has_writable();
        if (descriptor.get(vm.names.writable).value_or(Value(false)).to_boolean())
            attributes.set_writable();
        if (vm.exception())
            return false;
    }
    if (vm.exception())
        return {};

    dbgln_if(OBJECT_DEBUG, "Defining new property {} with data descriptor {{ attributes={}, value={} }}", property_name.to_display_string(), attributes, value);

    return define_property(property_name, value, attributes, throw_exceptions);
}

bool Object::define_property_without_transition(const PropertyName& property_name, Value value, PropertyAttributes attributes, bool throw_exceptions)
{
    TemporaryChange change(m_transitions_enabled, false);
    return define_property(property_name, value, attributes, throw_exceptions);
}

bool Object::define_property(const PropertyName& property_name, Value value, PropertyAttributes attributes, bool throw_exceptions)
{
    VERIFY(property_name.is_valid());

    if (property_name.is_number())
        return put_own_property_by_index(property_name.as_number(), value, attributes, PutOwnPropertyMode::DefineProperty, throw_exceptions);

    if (property_name.is_string() && property_name.string_may_be_number()) {
        i32 property_index = property_name.as_string().to_int().value_or(-1);
        if (property_index >= 0)
            return put_own_property_by_index(property_index, value, attributes, PutOwnPropertyMode::DefineProperty, throw_exceptions);
    }
    return put_own_property(property_name.to_string_or_symbol(), value, attributes, PutOwnPropertyMode::DefineProperty, throw_exceptions);
}

bool Object::define_native_accessor(PropertyName const& property_name, AK::Function<Value(VM&, GlobalObject&)> getter, AK::Function<Value(VM&, GlobalObject&)> setter, PropertyAttributes attribute)
{
    auto& vm = this->vm();
    String formatted_property_name;
    if (property_name.is_string()) {
        formatted_property_name = property_name.as_string();
    } else {
        formatted_property_name = String::formatted("[{}]", property_name.as_symbol()->description());
    }
    Function* getter_function = nullptr;
    if (getter) {
        auto name = String::formatted("get {}", formatted_property_name);
        getter_function = NativeFunction::create(global_object(), name, move(getter));
        getter_function->define_property_without_transition(vm.names.length, Value(0), Attribute::Configurable);
        if (vm.exception())
            return {};
        getter_function->define_property_without_transition(vm.names.name, js_string(vm.heap(), name), Attribute::Configurable);
        if (vm.exception())
            return {};
    }
    Function* setter_function = nullptr;
    if (setter) {
        auto name = String::formatted("set {}", formatted_property_name);
        setter_function = NativeFunction::create(global_object(), name, move(setter));
        setter_function->define_property_without_transition(vm.names.length, Value(1), Attribute::Configurable);
        if (vm.exception())
            return {};
        setter_function->define_property_without_transition(vm.names.name, js_string(vm.heap(), name), Attribute::Configurable);
        if (vm.exception())
            return {};
    }
    return define_accessor(property_name, getter_function, setter_function, attribute);
}

bool Object::define_accessor(const PropertyName& property_name, Function* getter, Function* setter, PropertyAttributes attributes, bool throw_exceptions)
{
    VERIFY(property_name.is_valid());

    Accessor* accessor { nullptr };
    auto property_metadata = shape().lookup(property_name.to_string_or_symbol());
    if (property_metadata.has_value()) {
        auto existing_property = get_direct(property_metadata.value().offset);
        if (existing_property.is_accessor())
            accessor = &existing_property.as_accessor();
    }
    if (!accessor) {
        accessor = Accessor::create(vm(), getter, setter);
        bool definition_success = define_property(property_name, accessor, attributes, throw_exceptions);
        if (vm().exception())
            return {};
        if (!definition_success)
            return false;
    } else {
        if (getter)
            accessor->set_getter(getter);
        if (setter)
            accessor->set_setter(setter);
    }
    return true;
}

bool Object::put_own_property(const StringOrSymbol& property_name, Value value, PropertyAttributes attributes, PutOwnPropertyMode mode, bool throw_exceptions)
{
    VERIFY(!(mode == PutOwnPropertyMode::Put && value.is_accessor()));

    if (value.is_accessor()) {
        auto& accessor = value.as_accessor();
        if (accessor.getter())
            attributes.set_has_getter();
        if (accessor.setter())
            attributes.set_has_setter();
    }

    // NOTE: We disable transitions during initialize(), this makes building common runtime objects significantly faster.
    //       Transitions are primarily interesting when scripts add properties to objects.
    if (!m_transitions_enabled && !m_shape->is_unique()) {
        m_shape->add_property_without_transition(property_name, attributes);
        m_storage.resize(m_shape->property_count());
        m_storage[m_shape->property_count() - 1] = value;
        return true;
    }

    auto metadata = shape().lookup(property_name);
    bool new_property = !metadata.has_value();

    if (!is_extensible() && new_property) {
        dbgln_if(OBJECT_DEBUG, "Disallow define_property of non-extensible object");
        if (throw_exceptions && vm().in_strict_mode())
            vm().throw_exception<TypeError>(global_object(), ErrorType::NonExtensibleDefine, property_name.to_display_string());
        return false;
    }

    if (new_property) {
        if (!m_shape->is_unique() && shape().property_count() > 100) {
            // If you add more than 100 properties to an object, let's stop doing
            // transitions to avoid filling up the heap with shapes.
            ensure_shape_is_unique();
        }

        if (m_shape->is_unique()) {
            m_shape->add_property_to_unique_shape(property_name, attributes);
            m_storage.resize(m_shape->property_count());
        } else if (m_transitions_enabled) {
            set_shape(*m_shape->create_put_transition(property_name, attributes));
        } else {
            m_shape->add_property_without_transition(property_name, attributes);
            m_storage.resize(m_shape->property_count());
        }
        metadata = shape().lookup(property_name);
        VERIFY(metadata.has_value());
    }

    auto value_here = m_storage[metadata.value().offset];
    if (!new_property && mode == PutOwnPropertyMode::DefineProperty && !metadata.value().attributes.is_configurable()) {
        if ((attributes.has_configurable() && attributes.is_configurable()) || (attributes.has_enumerable() && attributes.is_enumerable() != metadata.value().attributes.is_enumerable())) {
            dbgln_if(OBJECT_DEBUG, "Disallow reconfig of non-configurable property");
            if (throw_exceptions)
                vm().throw_exception<TypeError>(global_object(), ErrorType::DescChangeNonConfigurable, property_name.to_display_string());
            return false;
        }

        if (value_here.is_accessor() != value.is_accessor()) {
            dbgln_if(OBJECT_DEBUG, "Disallow reconfig of non-configurable property");
            if (throw_exceptions)
                vm().throw_exception<TypeError>(global_object(), ErrorType::DescChangeNonConfigurable, property_name.to_display_string());
            return false;
        }

        if (!value_here.is_accessor() && !metadata.value().attributes.is_writable() && ((attributes.has_writable() && attributes.is_writable()) || (!value.is_empty() && !same_value(value, value_here)))) {
            dbgln_if(OBJECT_DEBUG, "Disallow reconfig of non-configurable property");
            if (throw_exceptions)
                vm().throw_exception<TypeError>(global_object(), ErrorType::DescChangeNonConfigurable, property_name.to_display_string());
            return false;
        }

        if (value_here.is_accessor() && ((attributes.has_setter() && value.as_accessor().setter() != value_here.as_accessor().setter()) || (attributes.has_getter() && value.as_accessor().getter() != value_here.as_accessor().getter()))) {
            dbgln_if(OBJECT_DEBUG, "Disallow reconfig of non-configurable property");
            if (throw_exceptions)
                vm().throw_exception<TypeError>(global_object(), ErrorType::DescChangeNonConfigurable, property_name.to_display_string());
            return false;
        }
    }

    if (mode == PutOwnPropertyMode::DefineProperty && attributes != metadata.value().attributes) {
        if (m_shape->is_unique()) {
            m_shape->reconfigure_property_in_unique_shape(property_name, attributes);
        } else {
            set_shape(*m_shape->create_configure_transition(property_name, attributes));
        }
        metadata = shape().lookup(property_name);

        dbgln_if(OBJECT_DEBUG, "Reconfigured property {}, new shape says offset is {} and my storage capacity is {}", property_name.to_display_string(), metadata.value().offset, m_storage.size());
    }

    if (!new_property && mode == PutOwnPropertyMode::Put && !value_here.is_accessor() && !metadata.value().attributes.is_writable()) {
        dbgln_if(OBJECT_DEBUG, "Disallow write to non-writable property");
        if (throw_exceptions && vm().in_strict_mode())
            vm().throw_exception<TypeError>(global_object(), ErrorType::DescWriteNonWritable, property_name.to_display_string());
        return false;
    }

    if (value.is_empty())
        return true;

    if (value_here.is_native_property()) {
        call_native_property_setter(value_here.as_native_property(), this, value);
    } else {
        m_storage[metadata.value().offset] = value;
    }
    return true;
}

bool Object::put_own_property_by_index(u32 property_index, Value value, PropertyAttributes attributes, PutOwnPropertyMode mode, bool throw_exceptions)
{
    VERIFY(!(mode == PutOwnPropertyMode::Put && value.is_accessor()));

    auto existing_property = m_indexed_properties.get(nullptr, property_index, false);
    auto new_property = !existing_property.has_value();

    if (!is_extensible() && new_property) {
        dbgln_if(OBJECT_DEBUG, "Disallow define_property of non-extensible object");
        if (throw_exceptions && vm().in_strict_mode())
            vm().throw_exception<TypeError>(global_object(), ErrorType::NonExtensibleDefine, property_index);
        return false;
    }

    if (value.is_accessor()) {
        auto& accessor = value.as_accessor();
        if (accessor.getter())
            attributes.set_has_getter();
        if (accessor.setter())
            attributes.set_has_setter();
    }

    PropertyAttributes existing_attributes = new_property ? 0 : existing_property.value().attributes;

    if (!new_property && mode == PutOwnPropertyMode::DefineProperty && !existing_attributes.is_configurable() && attributes != existing_attributes) {
        dbgln_if(OBJECT_DEBUG, "Disallow reconfig of non-configurable property");
        if (throw_exceptions)
            vm().throw_exception<TypeError>(global_object(), ErrorType::DescChangeNonConfigurable, property_index);
        return false;
    }

    auto value_here = new_property ? Value() : existing_property.value().value;
    if (!new_property && mode == PutOwnPropertyMode::Put && !value_here.is_accessor() && !existing_attributes.is_writable()) {
        dbgln_if(OBJECT_DEBUG, "Disallow write to non-writable property");
        return false;
    }

    if (value.is_empty())
        return true;

    if (value_here.is_native_property()) {
        call_native_property_setter(value_here.as_native_property(), this, value);
    } else {
        m_indexed_properties.put(this, property_index, value, attributes, mode == PutOwnPropertyMode::Put);
    }
    return true;
}

bool Object::delete_property(const PropertyName& property_name)
{
    VERIFY(property_name.is_valid());

    if (property_name.is_number())
        return m_indexed_properties.remove(property_name.as_number());

    if (property_name.is_string() && property_name.string_may_be_number()) {
        i32 property_index = property_name.as_string().to_int().value_or(-1);
        if (property_index >= 0)
            return m_indexed_properties.remove(property_index);
    }

    auto metadata = shape().lookup(property_name.to_string_or_symbol());
    if (!metadata.has_value())
        return true;
    if (!metadata.value().attributes.is_configurable()) {
        if (vm().in_strict_mode())
            vm().throw_exception<TypeError>(global_object(), ErrorType::DescChangeNonConfigurable, property_name.to_string_or_symbol().to_display_string());
        return false;
    }

    size_t deleted_offset = metadata.value().offset;

    ensure_shape_is_unique();

    shape().remove_property_from_unique_shape(property_name.to_string_or_symbol(), deleted_offset);
    m_storage.remove(deleted_offset);
    return true;
}

void Object::ensure_shape_is_unique()
{
    if (shape().is_unique())
        return;

    m_shape = m_shape->create_unique_clone();
}

Value Object::get_by_index(u32 property_index) const
{
    const Object* object = this;
    while (object) {
        if (is<StringObject>(*object)) {
            auto& string = static_cast<const StringObject&>(*object).primitive_string().string();
            if (property_index < string.length())
                return js_string(heap(), string.substring(property_index, 1));
        } else if (static_cast<size_t>(property_index) < object->m_indexed_properties.array_like_size()) {
            auto result = object->m_indexed_properties.get(const_cast<Object*>(this), property_index);
            if (vm().exception())
                return {};
            if (result.has_value() && !result.value().value.is_empty())
                return result.value().value;
        }
        object = object->prototype();
        if (vm().exception())
            return {};
    }
    return {};
}

Value Object::get(const PropertyName& property_name, Value receiver, bool without_side_effects) const
{
    VERIFY(property_name.is_valid());

    if (property_name.is_number())
        return get_by_index(property_name.as_number());

    if (property_name.is_string() && property_name.string_may_be_number()) {
        auto& property_string = property_name.as_string();
        i32 property_index = property_string.to_int().value_or(-1);
        if (property_index >= 0)
            return get_by_index(property_index);
    }

    if (receiver.is_empty())
        receiver = Value(this);

    const Object* object = this;
    while (object) {
        auto value = object->get_own_property(property_name, receiver, without_side_effects);
        if (vm().exception())
            return {};
        if (!value.is_empty())
            return value;
        object = object->prototype();
        if (vm().exception())
            return {};
    }
    return {};
}

Value Object::get_without_side_effects(const PropertyName& property_name) const
{
    TemporaryClearException clear_exception(vm());
    return get(property_name, {}, true);
}

bool Object::put_by_index(u32 property_index, Value value)
{
    VERIFY(!value.is_empty());

    // If there's a setter in the prototype chain, we go to the setter.
    // Otherwise, it goes in the own property storage.
    Object* object = this;
    while (object) {
        auto existing_value = object->m_indexed_properties.get(nullptr, property_index, false);
        if (existing_value.has_value()) {
            auto value_here = existing_value.value();
            if (value_here.value.is_accessor()) {
                value_here.value.as_accessor().call_setter(object, value);
                return true;
            }
            if (value_here.value.is_native_property()) {
                // FIXME: Why doesn't put_by_index() receive the receiver value from put()?!
                auto receiver = this;
                call_native_property_setter(value_here.value.as_native_property(), receiver, value);
                return true;
            }
        }
        object = object->prototype();
        if (vm().exception())
            return {};
    }
    return put_own_property_by_index(property_index, value, default_attributes, PutOwnPropertyMode::Put);
}

bool Object::put(const PropertyName& property_name, Value value, Value receiver)
{
    VERIFY(property_name.is_valid());

    if (property_name.is_number())
        return put_by_index(property_name.as_number(), value);

    VERIFY(!value.is_empty());

    if (property_name.is_string() && property_name.string_may_be_number()) {
        auto& property_string = property_name.as_string();
        i32 property_index = property_string.to_int().value_or(-1);
        if (property_index >= 0)
            return put_by_index(property_index, value);
    }

    auto string_or_symbol = property_name.to_string_or_symbol();

    if (receiver.is_empty())
        receiver = Value(this);

    // If there's a setter in the prototype chain, we go to the setter.
    // Otherwise, it goes in the own property storage.
    Object* object = this;
    while (object) {
        auto metadata = object->shape().lookup(string_or_symbol);
        if (metadata.has_value()) {
            auto value_here = object->m_storage[metadata.value().offset];
            if (value_here.is_accessor()) {
                value_here.as_accessor().call_setter(receiver, value);
                return true;
            }
            if (value_here.is_native_property()) {
                call_native_property_setter(value_here.as_native_property(), receiver, value);
                return true;
            }
        }
        object = object->prototype();
        if (vm().exception())
            return false;
    }
    return put_own_property(string_or_symbol, value, default_attributes, PutOwnPropertyMode::Put);
}

bool Object::define_native_function(PropertyName const& property_name, AK::Function<Value(VM&, GlobalObject&)> native_function, i32 length, PropertyAttributes attribute)
{
    auto& vm = this->vm();
    String function_name;
    if (property_name.is_string()) {
        function_name = property_name.as_string();
    } else {
        function_name = String::formatted("[{}]", property_name.as_symbol()->description());
    }
    auto* function = NativeFunction::create(global_object(), function_name, move(native_function));
    function->define_property_without_transition(vm.names.length, Value(length), Attribute::Configurable);
    if (vm.exception())
        return {};
    function->define_property_without_transition(vm.names.name, js_string(vm.heap(), function_name), Attribute::Configurable);
    if (vm.exception())
        return {};
    return define_property(property_name, function, attribute);
}

bool Object::define_native_property(PropertyName const& property_name, AK::Function<Value(VM&, GlobalObject&)> getter, AK::Function<void(VM&, GlobalObject&, Value)> setter, PropertyAttributes attribute)
{
    return define_property(property_name, heap().allocate_without_global_object<NativeProperty>(move(getter), move(setter)), attribute);
}

// 20.1.2.3.1 ObjectDefineProperties ( O, Properties ), https://tc39.es/ecma262/#sec-objectdefineproperties
void Object::define_properties(Value properties)
{
    auto& vm = this->vm();
    auto* props = properties.to_object(global_object());
    if (!props)
        return;
    auto keys = props->get_own_properties(PropertyKind::Key);
    if (vm.exception())
        return;
    struct NameAndDescriptor {
        PropertyName name;
        PropertyDescriptor descriptor;
    };
    Vector<NameAndDescriptor> descriptors;
    for (auto& key : keys) {
        auto property_name = PropertyName::from_value(global_object(), key);
        auto property_descriptor = props->get_own_property_descriptor(property_name);
        if (property_descriptor.has_value() && property_descriptor->attributes.is_enumerable()) {
            auto descriptor_object = props->get(property_name);
            if (vm.exception())
                return;
            if (!descriptor_object.is_object()) {
                vm.throw_exception<TypeError>(global_object(), ErrorType::NotAnObject, descriptor_object.to_string_without_side_effects());
                return;
            }
            auto descriptor = PropertyDescriptor::from_dictionary(vm, descriptor_object.as_object());
            if (vm.exception())
                return;
            descriptors.append({ property_name, descriptor });
        }
    }
    for (auto& [name, descriptor] : descriptors) {
        // FIXME: The spec has both of this handled by DefinePropertyOrThrow(O, P, desc).
        //        We should invest some time in improving object property handling, it not being
        //        super close to the spec makes this and other things unnecessarily complicated.
        if (descriptor.is_accessor_descriptor())
            define_accessor(name, descriptor.getter, descriptor.setter, descriptor.attributes);
        else
            define_property(name, descriptor.value, descriptor.attributes);
    }
}

void Object::visit_edges(Cell::Visitor& visitor)
{
    Cell::visit_edges(visitor);
    visitor.visit(m_shape);

    for (auto& value : m_storage)
        visitor.visit(value);

    m_indexed_properties.for_each_value([&visitor](auto& value) {
        visitor.visit(value);
    });
}

bool Object::has_property(const PropertyName& property_name) const
{
    const Object* object = this;
    while (object) {
        if (object->has_own_property(property_name))
            return true;
        object = object->prototype();
        if (vm().exception())
            return false;
    }
    return false;
}

bool Object::has_own_property(const PropertyName& property_name) const
{
    VERIFY(property_name.is_valid());

    auto has_indexed_property = [&](u32 index) -> bool {
        if (is<StringObject>(*this))
            return index < static_cast<const StringObject*>(this)->primitive_string().string().length();
        return m_indexed_properties.has_index(index);
    };

    if (property_name.is_number())
        return has_indexed_property(property_name.as_number());

    if (property_name.is_string() && property_name.string_may_be_number()) {
        i32 property_index = property_name.as_string().to_int().value_or(-1);
        if (property_index >= 0)
            return has_indexed_property(property_index);
    }

    return shape().lookup(property_name.to_string_or_symbol()).has_value();
}

Value Object::ordinary_to_primitive(Value::PreferredType preferred_type) const
{
    VERIFY(preferred_type == Value::PreferredType::String || preferred_type == Value::PreferredType::Number);

    auto& vm = this->vm();

    Vector<FlyString, 2> method_names;
    if (preferred_type == Value::PreferredType::String)
        method_names = { vm.names.toString.as_string(), vm.names.valueOf.as_string() };
    else
        method_names = { vm.names.valueOf.as_string(), vm.names.toString.as_string() };

    for (auto& method_name : method_names) {
        auto method = get(method_name);
        if (vm.exception())
            return {};
        if (method.is_function()) {
            auto result = vm.call(method.as_function(), const_cast<Object*>(this));
            if (!result.is_object())
                return result;
        }
    }
    vm.throw_exception<TypeError>(global_object(), ErrorType::Convert, "object", preferred_type == Value::PreferredType::String ? "string" : "number");
    return {};
}

// 20.5.8.1 InstallErrorCause ( O, options ), https://tc39.es/proposal-error-cause/#sec-errorobjects-install-error-cause
void Object::install_error_cause(Value options)
{
    auto& vm = this->vm();
    if (!options.is_object())
        return;
    auto& options_object = options.as_object();
    if (!options_object.has_property(vm.names.cause))
        return;
    auto cause = options_object.get(vm.names.cause).value_or(js_undefined());
    if (vm.exception())
        return;
    define_property(vm.names.cause, cause, Attribute::Writable | Attribute::Configurable);
}

Value Object::invoke_internal(const StringOrSymbol& property_name, Optional<MarkedValueList> arguments)
{
    auto& vm = this->vm();
    auto property = get(property_name).value_or(js_undefined());
    if (vm.exception())
        return {};
    if (!property.is_function()) {
        vm.throw_exception<TypeError>(global_object(), ErrorType::NotAFunction, property.to_string_without_side_effects());
        return {};
    }
    return vm.call(property.as_function(), this, move(arguments));
}

Value Object::call_native_property_getter(NativeProperty& property, Value this_value) const
{
    auto& vm = this->vm();
    CallFrame call_frame;
    if (auto* interpreter = vm.interpreter_if_exists())
        call_frame.current_node = interpreter->current_node();
    call_frame.is_strict_mode = vm.in_strict_mode();
    call_frame.this_value = this_value;
    vm.push_call_frame(call_frame, global_object());
    if (vm.exception())
        return {};
    auto result = property.get(vm, global_object());
    vm.pop_call_frame();
    return result;
}

void Object::call_native_property_setter(NativeProperty& property, Value this_value, Value setter_value) const
{
    auto& vm = this->vm();
    CallFrame call_frame;
    if (auto* interpreter = vm.interpreter_if_exists())
        call_frame.current_node = interpreter->current_node();
    call_frame.is_strict_mode = vm.in_strict_mode();
    call_frame.this_value = this_value;
    vm.push_call_frame(call_frame, global_object());
    if (vm.exception())
        return;
    property.set(vm, global_object(), setter_value);
    vm.pop_call_frame();
}

}