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

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

#include <AK/CharacterTypes.h>
#include <AK/Function.h>
#include <AK/Optional.h>
#include <AK/TemporaryChange.h>
#include <AK/Utf16View.h>
#include <LibJS/Interpreter.h>
#include <LibJS/Parser.h>
#include <LibJS/Runtime/AbstractOperations.h>
#include <LibJS/Runtime/Accessor.h>
#include <LibJS/Runtime/ArgumentsObject.h>
#include <LibJS/Runtime/Array.h>
#include <LibJS/Runtime/BoundFunction.h>
#include <LibJS/Runtime/Completion.h>
#include <LibJS/Runtime/DeclarativeEnvironment.h>
#include <LibJS/Runtime/ECMAScriptFunctionObject.h>
#include <LibJS/Runtime/ErrorTypes.h>
#include <LibJS/Runtime/FunctionEnvironment.h>
#include <LibJS/Runtime/FunctionObject.h>
#include <LibJS/Runtime/GlobalObject.h>
#include <LibJS/Runtime/Object.h>
#include <LibJS/Runtime/ObjectEnvironment.h>
#include <LibJS/Runtime/PropertyDescriptor.h>
#include <LibJS/Runtime/PropertyName.h>
#include <LibJS/Runtime/ProxyObject.h>
#include <LibJS/Runtime/Reference.h>

namespace JS {

// 7.2.1 RequireObjectCoercible ( argument ), https://tc39.es/ecma262/#sec-requireobjectcoercible
ThrowCompletionOr<Value> require_object_coercible(GlobalObject& global_object, Value value)
{
    auto& vm = global_object.vm();
    if (value.is_nullish())
        return vm.throw_completion<TypeError>(global_object, ErrorType::NotObjectCoercible, value.to_string_without_side_effects());
    return value;
}

// 7.3.13 Call ( F, V [ , argumentsList ] ), https://tc39.es/ecma262/#sec-call
ThrowCompletionOr<Value> call_impl(GlobalObject& global_object, Value function, Value this_value, Optional<MarkedValueList> arguments_list)
{
    auto& vm = global_object.vm();

    // 1. If argumentsList is not present, set argumentsList to a new empty List.
    if (!arguments_list.has_value())
        arguments_list = MarkedValueList { global_object.heap() };

    // 2. If IsCallable(F) is false, throw a TypeError exception.
    if (!function.is_function())
        return vm.throw_completion<TypeError>(global_object, ErrorType::NotAFunction, function.to_string_without_side_effects());

    // 3. Return ? F.[[Call]](V, argumentsList).
    return function.as_function().internal_call(this_value, move(*arguments_list));
}

// 7.3.14 Construct ( F [ , argumentsList [ , newTarget ] ] ), https://tc39.es/ecma262/#sec-construct
ThrowCompletionOr<Object*> construct(GlobalObject& global_object, FunctionObject& function, Optional<MarkedValueList> arguments_list, FunctionObject* new_target)
{
    // 1. If newTarget is not present, set newTarget to F.
    if (!new_target)
        new_target = &function;

    // 2. If argumentsList is not present, set argumentsList to a new empty List.
    if (!arguments_list.has_value())
        arguments_list = MarkedValueList { global_object.heap() };

    // 3. Return ? F.[[Construct]](argumentsList, newTarget).
    return function.internal_construct(move(*arguments_list), *new_target);
}

// 7.3.18 LengthOfArrayLike ( obj ), https://tc39.es/ecma262/#sec-lengthofarraylike
ThrowCompletionOr<size_t> length_of_array_like(GlobalObject& global_object, Object const& object)
{
    auto& vm = global_object.vm();
    auto result = TRY(object.get(vm.names.length));
    auto length = result.to_length(global_object);
    if (auto* exception = vm.exception())
        return throw_completion(exception->value());
    return length;
}

// 7.3.19 CreateListFromArrayLike ( obj [ , elementTypes ] ), https://tc39.es/ecma262/#sec-createlistfromarraylike
ThrowCompletionOr<MarkedValueList> create_list_from_array_like(GlobalObject& global_object, Value value, Function<ThrowCompletionOr<void>(Value)> check_value)
{
    auto& vm = global_object.vm();
    auto& heap = global_object.heap();

    // 1. If elementTypes is not present, set elementTypes to « Undefined, Null, Boolean, String, Symbol, Number, BigInt, Object ».

    // 2. If Type(obj) is not Object, throw a TypeError exception.
    if (!value.is_object())
        return vm.throw_completion<TypeError>(global_object, ErrorType::NotAnObject, value.to_string_without_side_effects());

    auto& array_like = value.as_object();

    // 3. Let len be ? LengthOfArrayLike(obj).
    auto length = TRY(length_of_array_like(global_object, array_like));

    // 4. Let list be a new empty List.
    auto list = MarkedValueList { heap };

    // 5. Let index be 0.
    // 6. Repeat, while index < len,
    for (size_t i = 0; i < length; ++i) {
        // a. Let indexName be ! ToString(𝔽(index)).
        auto index_name = PropertyName { i };

        // b. Let next be ? Get(obj, indexName).
        auto next = TRY(array_like.get(index_name));

        // c. If Type(next) is not an element of elementTypes, throw a TypeError exception.
        if (check_value)
            TRY(check_value(next));

        // d. Append next as the last element of list.
        list.append(next);
    }

    // 7. Return list.
    return ThrowCompletionOr(move(list));
}

// 7.3.22 SpeciesConstructor ( O, defaultConstructor ), https://tc39.es/ecma262/#sec-speciesconstructor
ThrowCompletionOr<FunctionObject*> species_constructor(GlobalObject& global_object, Object const& object, FunctionObject& default_constructor)
{
    auto& vm = global_object.vm();

    // 1. Let C be ? Get(O, "constructor").
    auto constructor = TRY(object.get(vm.names.constructor));

    // 2. If C is undefined, return defaultConstructor.
    if (constructor.is_undefined())
        return &default_constructor;

    // 3. If Type(C) is not Object, throw a TypeError exception.
    if (!constructor.is_object())
        return vm.throw_completion<TypeError>(global_object, ErrorType::NotAConstructor, constructor.to_string_without_side_effects());

    // 4. Let S be ? Get(C, @@species).
    auto species = TRY(constructor.as_object().get(*vm.well_known_symbol_species()));

    // 5. If S is either undefined or null, return defaultConstructor.
    if (species.is_nullish())
        return &default_constructor;

    // 6. If IsConstructor(S) is true, return S.
    if (species.is_constructor())
        return &species.as_function();

    // 7. Throw a TypeError exception.
    return vm.throw_completion<TypeError>(global_object, ErrorType::NotAConstructor, species.to_string_without_side_effects());
}

// 7.3.24 GetFunctionRealm ( obj ), https://tc39.es/ecma262/#sec-getfunctionrealm
ThrowCompletionOr<Realm*> get_function_realm(GlobalObject& global_object, FunctionObject const& function)
{
    auto& vm = global_object.vm();

    // 1. Assert: ! IsCallable(obj) is true.

    // 2. If obj has a [[Realm]] internal slot, then
    if (function.realm()) {
        // a. Return obj.[[Realm]].
        return function.realm();
    }

    // 3. If obj is a bound function exotic object, then
    if (is<BoundFunction>(function)) {
        auto& bound_function = static_cast<BoundFunction const&>(function);

        // a. Let target be obj.[[BoundTargetFunction]].
        auto& target = bound_function.bound_target_function();

        // b. Return ? GetFunctionRealm(target).
        return get_function_realm(global_object, target);
    }

    // 4. If obj is a Proxy exotic object, then
    if (is<ProxyObject>(function)) {
        auto& proxy = static_cast<ProxyObject const&>(function);

        // a. If obj.[[ProxyHandler]] is null, throw a TypeError exception.
        if (proxy.is_revoked())
            return vm.throw_completion<TypeError>(global_object, ErrorType::ProxyRevoked);

        // b. Let proxyTarget be obj.[[ProxyTarget]].
        auto& proxy_target = proxy.target();

        // c. Return ? GetFunctionRealm(proxyTarget).
        VERIFY(proxy_target.is_function());
        return get_function_realm(global_object, static_cast<FunctionObject const&>(proxy_target));
    }

    // 5. Return the current Realm Record.
    return vm.current_realm();
}

// 10.1.6.2 IsCompatiblePropertyDescriptor ( Extensible, Desc, Current ), https://tc39.es/ecma262/#sec-iscompatiblepropertydescriptor
bool is_compatible_property_descriptor(bool extensible, PropertyDescriptor const& descriptor, Optional<PropertyDescriptor> const& current)
{
    // 1. Return ValidateAndApplyPropertyDescriptor(undefined, undefined, Extensible, Desc, Current).
    return validate_and_apply_property_descriptor(nullptr, {}, extensible, descriptor, current);
}

// 10.1.6.3 ValidateAndApplyPropertyDescriptor ( O, P, extensible, Desc, current ), https://tc39.es/ecma262/#sec-validateandapplypropertydescriptor
bool validate_and_apply_property_descriptor(Object* object, PropertyName const& property_name, bool extensible, PropertyDescriptor const& descriptor, Optional<PropertyDescriptor> const& current)
{
    // 1. Assert: If O is not undefined, then IsPropertyKey(P) is true.
    if (object)
        VERIFY(property_name.is_valid());

    // 2. If current is undefined, then
    if (!current.has_value()) {
        // a. If extensible is false, return false.
        if (!extensible)
            return false;

        // b. Assert: extensible is true.
        // c. If IsGenericDescriptor(Desc) is true or IsDataDescriptor(Desc) is true, then
        if (descriptor.is_generic_descriptor() || descriptor.is_data_descriptor()) {
            // i. If O is not undefined, create an own data property named P of object O whose [[Value]], [[Writable]],
            // [[Enumerable]], and [[Configurable]] attribute values are described by Desc.
            // If the value of an attribute field of Desc is absent, the attribute of the newly created property is set
            // to its default value.
            if (object) {
                auto value = descriptor.value.value_or(js_undefined());
                object->storage_set(property_name, { value, descriptor.attributes() });
            }
        }
        // d. Else,
        else {
            // i. Assert: ! IsAccessorDescriptor(Desc) is true.
            VERIFY(descriptor.is_accessor_descriptor());

            // ii. If O is not undefined, create an own accessor property named P of object O whose [[Get]], [[Set]],
            // [[Enumerable]], and [[Configurable]] attribute values are described by Desc.
            // If the value of an attribute field of Desc is absent, the attribute of the newly created property is set
            // to its default value.
            if (object) {
                auto accessor = Accessor::create(object->vm(), descriptor.get.value_or(nullptr), descriptor.set.value_or(nullptr));
                object->storage_set(property_name, { accessor, descriptor.attributes() });
            }
        }
        // e. Return true.
        return true;
    }

    // 3. If every field in Desc is absent, return true.
    if (descriptor.is_empty())
        return true;

    // 4. If current.[[Configurable]] is false, then
    if (!*current->configurable) {
        // a. If Desc.[[Configurable]] is present and its value is true, return false.
        if (descriptor.configurable.has_value() && *descriptor.configurable)
            return false;

        // b. If Desc.[[Enumerable]] is present and ! SameValue(Desc.[[Enumerable]], current.[[Enumerable]]) is false, return false.
        if (descriptor.enumerable.has_value() && *descriptor.enumerable != *current->enumerable)
            return false;
    }

    // 5. If ! IsGenericDescriptor(Desc) is true, then
    if (descriptor.is_generic_descriptor()) {
        // a. NOTE: No further validation is required.
    }
    // 6. Else if ! SameValue(! IsDataDescriptor(current), ! IsDataDescriptor(Desc)) is false, then
    else if (current->is_data_descriptor() != descriptor.is_data_descriptor()) {
        // a. If current.[[Configurable]] is false, return false.
        if (!*current->configurable)
            return false;

        // b. If IsDataDescriptor(current) is true, then
        if (current->is_data_descriptor()) {
            // If O is not undefined, convert the property named P of object O from a data property to an accessor property.
            // Preserve the existing values of the converted property's [[Configurable]] and [[Enumerable]] attributes and
            // set the rest of the property's attributes to their default values.
            if (object) {
                auto accessor = Accessor::create(object->vm(), nullptr, nullptr);
                object->storage_set(property_name, { accessor, current->attributes() });
            }
        }
        // c. Else,
        else {
            // If O is not undefined, convert the property named P of object O from an accessor property to a data property.
            // Preserve the existing values of the converted property's [[Configurable]] and [[Enumerable]] attributes and
            // set the rest of the property's attributes to their default values.
            if (object) {
                auto value = js_undefined();
                object->storage_set(property_name, { value, current->attributes() });
            }
        }
    }
    // 7. Else if IsDataDescriptor(current) and IsDataDescriptor(Desc) are both true, then
    else if (current->is_data_descriptor() && descriptor.is_data_descriptor()) {
        // a. If current.[[Configurable]] is false and current.[[Writable]] is false, then
        if (!*current->configurable && !*current->writable) {
            // i. If Desc.[[Writable]] is present and Desc.[[Writable]] is true, return false.
            if (descriptor.writable.has_value() && *descriptor.writable)
                return false;

            // ii. If Desc.[[Value]] is present and SameValue(Desc.[[Value]], current.[[Value]]) is false, return false.
            if (descriptor.value.has_value() && !same_value(*descriptor.value, *current->value))
                return false;

            // iii. Return true.
            return true;
        }
    }
    // 8. Else,
    else {
        // a. Assert: ! IsAccessorDescriptor(current) and ! IsAccessorDescriptor(Desc) are both true.
        VERIFY(current->is_accessor_descriptor());
        VERIFY(descriptor.is_accessor_descriptor());

        // b. If current.[[Configurable]] is false, then
        if (!*current->configurable) {
            // i. If Desc.[[Set]] is present and SameValue(Desc.[[Set]], current.[[Set]]) is false, return false.
            if (descriptor.set.has_value() && *descriptor.set != *current->set)
                return false;

            // ii. If Desc.[[Get]] is present and SameValue(Desc.[[Get]], current.[[Get]]) is false, return false.
            if (descriptor.get.has_value() && *descriptor.get != *current->get)
                return false;

            // iii. Return true.
            return true;
        }
    }

    // 9. If O is not undefined, then
    if (object) {
        // a. For each field of Desc that is present, set the corresponding attribute of the property named P of object O to the value of the field.
        Value value;
        if (descriptor.is_accessor_descriptor() || (current->is_accessor_descriptor() && !descriptor.is_data_descriptor())) {
            auto* getter = descriptor.get.value_or(current->get.value_or(nullptr));
            auto* setter = descriptor.set.value_or(current->set.value_or(nullptr));
            value = Accessor::create(object->vm(), getter, setter);
        } else {
            value = descriptor.value.value_or(current->value.value_or({}));
        }
        PropertyAttributes attributes;
        attributes.set_writable(descriptor.writable.value_or(current->writable.value_or(false)));
        attributes.set_enumerable(descriptor.enumerable.value_or(current->enumerable.value_or(false)));
        attributes.set_configurable(descriptor.configurable.value_or(current->configurable.value_or(false)));
        object->storage_set(property_name, { value, attributes });
    }

    // 10. Return true.
    return true;
}

// 10.1.14 GetPrototypeFromConstructor ( constructor, intrinsicDefaultProto ), https://tc39.es/ecma262/#sec-getprototypefromconstructor
ThrowCompletionOr<Object*> get_prototype_from_constructor(GlobalObject& global_object, FunctionObject const& constructor, Object* (GlobalObject::*intrinsic_default_prototype)())
{
    auto& vm = global_object.vm();

    // 1. Assert: intrinsicDefaultProto is this specification's name of an intrinsic object. The corresponding object must be an intrinsic that is intended to be used as the [[Prototype]] value of an object.

    // 2. Let proto be ? Get(constructor, "prototype").
    auto prototype = TRY(constructor.get(vm.names.prototype));

    // 3. If Type(proto) is not Object, then
    if (!prototype.is_object()) {
        // a. Let realm be ? GetFunctionRealm(constructor).
        auto* realm = TRY(get_function_realm(global_object, constructor));

        // b. Set proto to realm's intrinsic object named intrinsicDefaultProto.
        prototype = (realm->global_object().*intrinsic_default_prototype)();
    }

    // 4. Return proto.
    return &prototype.as_object();
}

// 9.1.2.2 NewDeclarativeEnvironment ( E ), https://tc39.es/ecma262/#sec-newdeclarativeenvironment
DeclarativeEnvironment* new_declarative_environment(Environment& environment)
{
    auto& global_object = environment.global_object();
    return global_object.heap().allocate<DeclarativeEnvironment>(global_object, &environment);
}

// 9.1.2.3 NewObjectEnvironment ( O, W, E ), https://tc39.es/ecma262/#sec-newobjectenvironment
ObjectEnvironment* new_object_environment(Object& object, bool is_with_environment, Environment* environment)
{
    auto& global_object = object.global_object();
    return global_object.heap().allocate<ObjectEnvironment>(global_object, object, is_with_environment ? ObjectEnvironment::IsWithEnvironment::Yes : ObjectEnvironment::IsWithEnvironment::No, environment);
}

// 9.1.2.4 NewFunctionEnvironment ( F, newTarget ), https://tc39.es/ecma262/#sec-newfunctionenvironment
FunctionEnvironment* new_function_environment(ECMAScriptFunctionObject& function, Object* new_target)
{
    auto& global_object = function.global_object();

    // 1. Let env be a new function Environment Record containing no bindings.
    auto* env = global_object.heap().allocate<FunctionEnvironment>(global_object, function.environment());

    // 2. Set env.[[FunctionObject]] to F.
    env->set_function_object(function);

    // 3. If F.[[ThisMode]] is lexical, set env.[[ThisBindingStatus]] to lexical.
    if (function.this_mode() == ECMAScriptFunctionObject::ThisMode::Lexical)
        env->set_this_binding_status(FunctionEnvironment::ThisBindingStatus::Lexical);
    // 4. Else, set env.[[ThisBindingStatus]] to uninitialized.
    else
        env->set_this_binding_status(FunctionEnvironment::ThisBindingStatus::Uninitialized);

    // 5. Set env.[[NewTarget]] to newTarget.
    env->set_new_target(new_target ?: js_undefined());

    // 6. Set env.[[OuterEnv]] to F.[[Environment]].
    // NOTE: Done in step 1 via the FunctionEnvironment constructor.

    // 7. Return env.
    return env;
}

// 9.4.3 GetThisEnvironment ( ), https://tc39.es/ecma262/#sec-getthisenvironment
Environment& get_this_environment(VM& vm)
{
    for (auto* env = vm.lexical_environment(); env; env = env->outer_environment()) {
        if (env->has_this_binding())
            return *env;
    }
    VERIFY_NOT_REACHED();
}

// 13.3.7.2 GetSuperConstructor ( ), https://tc39.es/ecma262/#sec-getsuperconstructor
Object* get_super_constructor(VM& vm)
{
    // 1. Let envRec be GetThisEnvironment().
    auto& env = get_this_environment(vm);

    // 2. Assert: envRec is a function Environment Record.
    // 3. Let activeFunction be envRec.[[FunctionObject]].
    // 4. Assert: activeFunction is an ECMAScript function object.
    auto& active_function = verify_cast<FunctionEnvironment>(env).function_object();

    // 5. Let superConstructor be ! activeFunction.[[GetPrototypeOf]]().
    auto* super_constructor = MUST(active_function.internal_get_prototype_of());

    // 6. Return superConstructor.
    return super_constructor;
}

// 13.3.7.3 MakeSuperPropertyReference ( actualThis, propertyKey, strict ), https://tc39.es/ecma262/#sec-makesuperpropertyreference
ThrowCompletionOr<Reference> make_super_property_reference(GlobalObject& global_object, Value actual_this, StringOrSymbol const& property_key, bool strict)
{
    auto& vm = global_object.vm();
    // 1. Let env be GetThisEnvironment().
    auto& env = verify_cast<FunctionEnvironment>(get_this_environment(vm));
    // 2. Assert: env.HasSuperBinding() is true.
    VERIFY(env.has_super_binding());
    // 3. Let baseValue be ? env.GetSuperBase().
    auto base_value = TRY(env.get_super_base());
    // 4. Let bv be ? RequireObjectCoercible(baseValue).
    auto bv = TRY(require_object_coercible(global_object, base_value));
    // 5. Return the Reference Record { [[Base]]: bv, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: actualThis }.
    // 6. NOTE: This returns a Super Reference Record.
    return Reference { bv, property_key, actual_this, strict };
}

// 19.2.1.1 PerformEval ( x, callerRealm, strictCaller, direct ), https://tc39.es/ecma262/#sec-performeval
ThrowCompletionOr<Value> perform_eval(Value x, GlobalObject& caller_realm, CallerMode strict_caller, EvalMode direct)
{
    VERIFY(direct == EvalMode::Direct || strict_caller == CallerMode::NonStrict);
    if (!x.is_string())
        return x;

    auto& vm = caller_realm.vm();
    auto& eval_realm = vm.running_execution_context().realm;

    auto& code_string = x.as_string();
    Parser parser { Lexer { code_string.string() } };
    auto program = parser.parse_program(strict_caller == CallerMode::Strict);

    if (parser.has_errors()) {
        auto& error = parser.errors()[0];
        return vm.throw_completion<SyntaxError>(caller_realm, error.to_string());
    }

    auto strict_eval = strict_caller == CallerMode::Strict;
    if (program->is_strict_mode())
        strict_eval = true;

    auto& running_context = vm.running_execution_context();

    Environment* lexical_environment;
    Environment* variable_environment;
    if (direct == EvalMode::Direct) {
        lexical_environment = new_declarative_environment(*running_context.lexical_environment);
        variable_environment = running_context.variable_environment;
    } else {
        lexical_environment = new_declarative_environment(eval_realm->global_environment());
        variable_environment = &eval_realm->global_environment();
    }

    if (strict_eval)
        variable_environment = lexical_environment;

    if (direct == EvalMode::Direct && !strict_eval) {
        // NOTE: Non-strict direct eval() forces us to deoptimize variable accesses.
        //       Mark the variable environment chain as screwed since we will not be able
        //       to rely on cached environment coordinates from this point on.
        variable_environment->set_permanently_screwed_by_eval();
    }

    // 18. If runningContext is not already suspended, suspend runningContext.
    // FIXME: We don't have this concept yet.

    ExecutionContext eval_context(vm.heap());
    eval_context.realm = eval_realm;
    eval_context.variable_environment = variable_environment;
    eval_context.lexical_environment = lexical_environment;
    vm.push_execution_context(eval_context, eval_realm->global_object());

    ScopeGuard pop_guard = [&] {
        vm.pop_execution_context();
    };

    TRY(eval_declaration_instantiation(vm, eval_realm->global_object(), program, variable_environment, lexical_environment, strict_eval));

    auto& interpreter = vm.interpreter();
    TemporaryChange scope_change_strict(vm.running_execution_context().is_strict_mode, strict_eval);
    // Note: We specifically use evaluate_statements here since we don't want to use global_declaration_instantiation from Program::execute.
    auto eval_result = program->evaluate_statements(interpreter, caller_realm);

    if (auto* exception = vm.exception())
        return throw_completion(exception->value());
    else
        return eval_result.value_or(js_undefined());
}

// 19.2.1.3 EvalDeclarationInstantiation ( body, varEnv, lexEnv, privateEnv, strict ), https://tc39.es/ecma262/#sec-evaldeclarationinstantiation
ThrowCompletionOr<void> eval_declaration_instantiation(VM& vm, GlobalObject& global_object, Program const& program, Environment* variable_environment, Environment* lexical_environment, bool strict)
{
    // FIXME: I'm not sure if the global object is correct here. And this is quite a crucial spot!
    GlobalEnvironment* global_var_environment = variable_environment->is_global_environment() ? static_cast<GlobalEnvironment*>(variable_environment) : nullptr;

    if (!strict) {
        if (global_var_environment) {
            program.for_each_var_declared_name([&](auto const& name) {
                if (global_var_environment->has_lexical_declaration(name)) {
                    vm.throw_exception<SyntaxError>(global_object, ErrorType::FixmeAddAnErrorStringWithMessage, "Var already declared lexically");
                    return IterationDecision::Break;
                }
                return IterationDecision::Continue;
            });
        }

        auto* this_environment = lexical_environment;
        while (this_environment != variable_environment) {
            if (!is<ObjectEnvironment>(*this_environment)) {
                program.for_each_var_declared_name([&](auto const& name) {
                    if (MUST(this_environment->has_binding(name))) {
                        vm.throw_exception<SyntaxError>(global_object, ErrorType::FixmeAddAnErrorStringWithMessage, "Var already declared lexically");
                        return IterationDecision::Break;
                    }
                    // FIXME: NOTE: Annex B.3.4 defines alternate semantics for the above step.
                    // In particular it only throw the syntax error if it is not an environment from a catchclause.
                    return IterationDecision::Continue;
                });
                if (auto* exception = vm.exception())
                    return throw_completion(exception->value());
            }

            this_environment = this_environment->outer_environment();
            VERIFY(this_environment);
        }
    }

    HashTable<FlyString> declared_function_names;
    Vector<FunctionDeclaration const&> functions_to_initialize;
    program.for_each_var_function_declaration_in_reverse_order([&](FunctionDeclaration const& function) {
        if (declared_function_names.set(function.name()) != AK::HashSetResult::InsertedNewEntry)
            return IterationDecision::Continue;

        if (global_var_environment) {
            auto function_definable = global_var_environment->can_declare_global_function(function.name());
            if (vm.exception())
                return IterationDecision::Break;
            if (!function_definable) {
                vm.throw_exception<TypeError>(global_object, ErrorType::FixmeAddAnErrorStringWithMessage, "Cannot define global function");
                return IterationDecision::Break;
            }
        }
        functions_to_initialize.append(function);
        return IterationDecision::Continue;
    });

    if (auto* exception = vm.exception())
        return throw_completion(exception->value());

    if (!strict) {
        // The spec here uses 'declaredVarNames' but that has not been declared yet.
        HashTable<FlyString> hoisted_functions;
        program.for_each_function_hoistable_with_annexB_extension([&](FunctionDeclaration& function_declaration) {
            auto& function_name = function_declaration.name();
            auto* this_environment = lexical_environment;

            while (this_environment != variable_environment) {
                if (!is<ObjectEnvironment>(*this_environment) && MUST(this_environment->has_binding(function_name)))
                    return IterationDecision::Continue;

                this_environment = this_environment->outer_environment();
                VERIFY(this_environment);
            }

            if (global_var_environment) {
                if (global_var_environment->has_lexical_declaration(function_name))
                    return IterationDecision::Continue;
                auto var_definable = global_var_environment->can_declare_global_var(function_name);
                if (vm.exception())
                    return IterationDecision::Break;
                if (!var_definable)
                    return IterationDecision::Continue;
            }

            if (!declared_function_names.contains(function_name) && !hoisted_functions.contains(function_name)) {
                if (global_var_environment) {
                    global_var_environment->create_global_var_binding(function_name, true);
                    if (vm.exception())
                        return IterationDecision::Break;
                } else {
                    if (!MUST(variable_environment->has_binding(function_name))) {
                        MUST(variable_environment->create_mutable_binding(global_object, function_name, true));
                        MUST(variable_environment->initialize_binding(global_object, function_name, js_undefined()));
                    }
                }

                hoisted_functions.set(function_name);
            }

            function_declaration.set_should_do_additional_annexB_steps();

            return IterationDecision::Continue;
        });

        if (auto* exception = vm.exception())
            return throw_completion(exception->value());
    }

    HashTable<FlyString> declared_var_names;

    program.for_each_var_scoped_variable_declaration([&](VariableDeclaration const& declaration) {
        declaration.for_each_bound_name([&](auto const& name) {
            if (!declared_function_names.contains(name)) {
                if (global_var_environment) {
                    auto variable_definable = global_var_environment->can_declare_global_var(name);
                    if (vm.exception())
                        return IterationDecision::Break;
                    if (!variable_definable) {
                        vm.throw_exception<TypeError>(global_object, ErrorType::FixmeAddAnErrorStringWithMessage, "Cannot define global var");
                        return IterationDecision::Break;
                    }
                }
                declared_var_names.set(name);
            }
            return IterationDecision::Continue;
        });
        if (vm.exception())
            return IterationDecision::Break;
        return IterationDecision::Continue;
    });

    if (auto* exception = vm.exception())
        return throw_completion(exception->value());

    // 14. NOTE: No abnormal terminations occur after this algorithm step unless varEnv is a global Environment Record and the global object is a Proxy exotic object.

    program.for_each_lexically_scoped_declaration([&](Declaration const& declaration) {
        declaration.for_each_bound_name([&](auto const& name) {
            if (declaration.is_constant_declaration())
                (void)lexical_environment->create_immutable_binding(global_object, name, true);
            else
                (void)lexical_environment->create_mutable_binding(global_object, name, false);
            if (vm.exception())
                return IterationDecision::Break;
            return IterationDecision::Continue;
        });
        if (vm.exception())
            return IterationDecision::Break;
        return IterationDecision::Continue;
    });

    if (auto* exception = vm.exception())
        return throw_completion(exception->value());

    for (auto& declaration : functions_to_initialize) {
        auto* function = ECMAScriptFunctionObject::create(global_object, declaration.name(), declaration.body(), declaration.parameters(), declaration.function_length(), lexical_environment, declaration.kind(), declaration.is_strict_mode(), declaration.might_need_arguments_object());
        if (global_var_environment) {
            global_var_environment->create_global_function_binding(declaration.name(), function, true);
            if (auto* exception = vm.exception())
                return throw_completion(exception->value());
        } else {
            auto binding_exists = MUST(variable_environment->has_binding(declaration.name()));

            if (!binding_exists) {
                TRY(variable_environment->create_mutable_binding(global_object, declaration.name(), true));
                TRY(variable_environment->initialize_binding(global_object, declaration.name(), function));
            } else {
                variable_environment->set_mutable_binding(global_object, declaration.name(), function, false);
                if (auto* exception = vm.exception())
                    return throw_completion(exception->value());
            }
        }
    }

    for (auto& var_name : declared_var_names) {
        if (global_var_environment) {
            global_var_environment->create_global_var_binding(var_name, true);
            if (auto* exception = vm.exception())
                return throw_completion(exception->value());
        } else {
            auto binding_exists = MUST(variable_environment->has_binding(var_name));

            if (!binding_exists) {
                TRY(variable_environment->create_mutable_binding(global_object, var_name, true));
                TRY(variable_environment->initialize_binding(global_object, var_name, js_undefined()));
            }
        }
    }

    return {};
}

// 10.4.4.6 CreateUnmappedArgumentsObject ( argumentsList ), https://tc39.es/ecma262/#sec-createunmappedargumentsobject
Object* create_unmapped_arguments_object(GlobalObject& global_object, Span<Value> arguments)
{
    auto& vm = global_object.vm();

    // 1. Let len be the number of elements in argumentsList.
    auto length = arguments.size();

    // 2. Let obj be ! OrdinaryObjectCreate(%Object.prototype%, « [[ParameterMap]] »).
    // 3. Set obj.[[ParameterMap]] to undefined.
    auto* object = Object::create(global_object, global_object.object_prototype());
    object->set_has_parameter_map();

    // 4. Perform DefinePropertyOrThrow(obj, "length", PropertyDescriptor { [[Value]]: 𝔽(len), [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true }).
    MUST(object->define_property_or_throw(vm.names.length, { .value = Value(length), .writable = true, .enumerable = false, .configurable = true }));

    // 5. Let index be 0.
    // 6. Repeat, while index < len,
    for (size_t index = 0; index < length; ++index) {
        // a. Let val be argumentsList[index].
        auto value = arguments[index];

        // b. Perform ! CreateDataPropertyOrThrow(obj, ! ToString(𝔽(index)), val).
        MUST(object->create_data_property_or_throw(index, value));

        // c. Set index to index + 1.
    }

    // 7. Perform ! DefinePropertyOrThrow(obj, @@iterator, PropertyDescriptor { [[Value]]: %Array.prototype.values%, [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true }).
    auto* array_prototype_values = global_object.array_prototype_values_function();
    MUST(object->define_property_or_throw(*vm.well_known_symbol_iterator(), { .value = array_prototype_values, .writable = true, .enumerable = false, .configurable = true }));

    // 8. Perform ! DefinePropertyOrThrow(obj, "callee", PropertyDescriptor { [[Get]]: %ThrowTypeError%, [[Set]]: %ThrowTypeError%, [[Enumerable]]: false, [[Configurable]]: false }).
    auto* throw_type_error = global_object.throw_type_error_function();
    MUST(object->define_property_or_throw(vm.names.callee, { .get = throw_type_error, .set = throw_type_error, .enumerable = false, .configurable = false }));

    // 9. Return obj.
    return object;
}

// 10.4.4.7 CreateMappedArgumentsObject ( func, formals, argumentsList, env ), https://tc39.es/ecma262/#sec-createmappedargumentsobject
Object* create_mapped_arguments_object(GlobalObject& global_object, FunctionObject& function, Vector<FunctionNode::Parameter> const& formals, Span<Value> arguments, Environment& environment)
{
    auto& vm = global_object.vm();

    // 1. Assert: formals does not contain a rest parameter, any binding patterns, or any initializers. It may contain duplicate identifiers.

    // 2. Let len be the number of elements in argumentsList.
    VERIFY(arguments.size() <= NumericLimits<i32>::max());
    i32 length = static_cast<i32>(arguments.size());

    // 3. Let obj be ! MakeBasicObject(« [[Prototype]], [[Extensible]], [[ParameterMap]] »).
    // 4. Set obj.[[GetOwnProperty]] as specified in 10.4.4.1.
    // 5. Set obj.[[DefineOwnProperty]] as specified in 10.4.4.2.
    // 6. Set obj.[[Get]] as specified in 10.4.4.3.
    // 7. Set obj.[[Set]] as specified in 10.4.4.4.
    // 8. Set obj.[[Delete]] as specified in 10.4.4.5.
    // 9. Set obj.[[Prototype]] to %Object.prototype%.
    auto* object = vm.heap().allocate<ArgumentsObject>(global_object, global_object, environment);
    VERIFY(!vm.exception());

    // 14. Let index be 0.
    // 15. Repeat, while index < len,
    for (i32 index = 0; index < length; ++index) {
        // a. Let val be argumentsList[index].
        auto value = arguments[index];

        // b. Perform ! CreateDataPropertyOrThrow(obj, ! ToString(𝔽(index)), val).
        MUST(object->create_data_property_or_throw(index, value));

        // c. Set index to index + 1.
    }

    // 16. Perform ! DefinePropertyOrThrow(obj, "length", PropertyDescriptor { [[Value]]: 𝔽(len), [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true }).
    MUST(object->define_property_or_throw(vm.names.length, { .value = Value(length), .writable = true, .enumerable = false, .configurable = true }));

    // 17. Let mappedNames be a new empty List.
    HashTable<FlyString> mapped_names;

    // 18. Set index to numberOfParameters - 1.
    // 19. Repeat, while index ≥ 0,
    VERIFY(formals.size() <= NumericLimits<i32>::max());
    for (i32 index = static_cast<i32>(formals.size()) - 1; index >= 0; --index) {
        // a. Let name be parameterNames[index].
        auto const& name = formals[index].binding.get<FlyString>();

        // b. If name is not an element of mappedNames, then
        if (mapped_names.contains(name))
            continue;

        // i. Add name as an element of the list mappedNames.
        mapped_names.set(name);

        // ii. If index < len, then
        if (index < length) {
            // 1. Let g be MakeArgGetter(name, env).
            // 2. Let p be MakeArgSetter(name, env).
            // 3. Perform map.[[DefineOwnProperty]](! ToString(𝔽(index)), PropertyDescriptor { [[Set]]: p, [[Get]]: g, [[Enumerable]]: false, [[Configurable]]: true }).
            object->parameter_map().define_native_accessor(
                PropertyName { index },
                [&environment, name](VM&, GlobalObject& global_object_getter) -> Value {
                    return environment.get_binding_value(global_object_getter, name, false);
                },
                [&environment, name](VM& vm, GlobalObject& global_object_setter) {
                    environment.set_mutable_binding(global_object_setter, name, vm.argument(0), false);
                    return js_undefined();
                },
                Attribute::Configurable);
        }
    }

    // 20. Perform ! DefinePropertyOrThrow(obj, @@iterator, PropertyDescriptor { [[Value]]: %Array.prototype.values%, [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true }).
    auto* array_prototype_values = global_object.array_prototype_values_function();
    MUST(object->define_property_or_throw(*vm.well_known_symbol_iterator(), { .value = array_prototype_values, .writable = true, .enumerable = false, .configurable = true }));

    // 21. Perform ! DefinePropertyOrThrow(obj, "callee", PropertyDescriptor { [[Value]]: func, [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true }).
    MUST(object->define_property_or_throw(vm.names.callee, { .value = &function, .writable = true, .enumerable = false, .configurable = true }));

    // 22. Return obj.
    return object;
}

// 7.1.21 CanonicalNumericIndexString ( argument ), https://tc39.es/ecma262/#sec-canonicalnumericindexstring
Value canonical_numeric_index_string(GlobalObject& global_object, PropertyName const& property_name)
{
    // NOTE: If the property name is a number type (An implementation-defined optimized
    // property key type), it can be treated as a string property that has already been
    // converted successfully into a canonical numeric index.

    VERIFY(property_name.is_string() || property_name.is_number());

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

    // 1. Assert: Type(argument) is String.
    auto argument = Value(js_string(global_object.vm(), property_name.as_string()));

    // 2. If argument is "-0", return -0𝔽.
    if (argument.as_string().string() == "-0")
        return Value(-0.0);

    // 3. Let n be ! ToNumber(argument).
    auto n = argument.to_number(global_object);

    // 4. If SameValue(! ToString(n), argument) is false, return undefined.
    if (!same_value(n.to_primitive_string(global_object), argument))
        return js_undefined();

    // 5. Return n.
    return n;
}

// 22.1.3.17.1 GetSubstitution ( matched, str, position, captures, namedCaptures, replacement ), https://tc39.es/ecma262/#sec-getsubstitution
ThrowCompletionOr<String> get_substitution(GlobalObject& global_object, Utf16View const& matched, Utf16View const& str, size_t position, Span<Value> captures, Value named_captures, Value replacement)
{
    auto& vm = global_object.vm();

    auto replace_string = replacement.to_utf16_string(global_object);
    if (auto* exception = vm.exception())
        return throw_completion(exception->value());
    auto replace_view = replace_string.view();

    StringBuilder result;

    for (size_t i = 0; i < replace_view.length_in_code_units(); ++i) {
        u16 curr = replace_view.code_unit_at(i);

        if ((curr != '$') || (i + 1 >= replace_view.length_in_code_units())) {
            result.append(curr);
            continue;
        }

        u16 next = replace_view.code_unit_at(i + 1);

        if (next == '$') {
            result.append('$');
            ++i;
        } else if (next == '&') {
            result.append(matched);
            ++i;
        } else if (next == '`') {
            auto substring = str.substring_view(0, position);
            result.append(substring);
            ++i;
        } else if (next == '\'') {
            auto tail_pos = position + matched.length_in_code_units();
            if (tail_pos < str.length_in_code_units()) {
                auto substring = str.substring_view(tail_pos);
                result.append(substring);
            }
            ++i;
        } else if (is_ascii_digit(next)) {
            bool is_two_digits = (i + 2 < replace_view.length_in_code_units()) && is_ascii_digit(replace_view.code_unit_at(i + 2));

            auto capture_postition_string = replace_view.substring_view(i + 1, is_two_digits ? 2 : 1).to_utf8();
            auto capture_position = capture_postition_string.to_uint();

            if (capture_position.has_value() && (*capture_position > 0) && (*capture_position <= captures.size())) {
                auto& value = captures[*capture_position - 1];

                if (!value.is_undefined()) {
                    auto value_string = value.to_string(global_object);
                    if (auto* exception = vm.exception())
                        return throw_completion(exception->value());

                    result.append(value_string);
                }

                i += is_two_digits ? 2 : 1;
            } else {
                result.append(curr);
            }
        } else if (next == '<') {
            auto start_position = i + 2;
            Optional<size_t> end_position;

            for (size_t j = start_position; j < replace_view.length_in_code_units(); ++j) {
                if (replace_view.code_unit_at(j) == '>') {
                    end_position = j;
                    break;
                }
            }

            if (named_captures.is_undefined() || !end_position.has_value()) {
                result.append(curr);
            } else {
                auto group_name_view = replace_view.substring_view(start_position, *end_position - start_position);
                auto group_name = group_name_view.to_utf8(Utf16View::AllowInvalidCodeUnits::Yes);

                auto capture = TRY(named_captures.as_object().get(group_name));

                if (!capture.is_undefined()) {
                    auto capture_string = capture.to_string(global_object);
                    if (auto* exception = vm.exception())
                        return throw_completion(exception->value());

                    result.append(capture_string);
                }

                i = *end_position;
            }
        } else {
            result.append(curr);
        }
    }

    return result.build();
}

}