LibJS: Convert NativeFunction callback to ThrowCompletionOr

13 files changed, 91 insertions, 65 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/GlobalObject.cpp b/Userland/Libraries/LibJS/Runtime/GlobalObject.cpp
index 8b8410495d..9c2e8c6147 100644
--- a/Userland/Libraries/LibJS/Runtime/GlobalObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/GlobalObject.cpp
@@ -201,8 +201,7 @@ void GlobalObject::initialize_global_object()
 
     // 10.2.4.1 %ThrowTypeError% ( ), https://tc39.es/ecma262/#sec-%throwtypeerror%
     m_throw_type_error_function = NativeFunction::create(global_object(), {}, [](VM& vm, GlobalObject& global_object) {
-        vm.throw_exception<TypeError>(global_object, ErrorType::RestrictedFunctionPropertiesAccess);
-        return Value();
+        return vm.throw_completion<TypeError>(global_object, ErrorType::RestrictedFunctionPropertiesAccess);
     });
     m_throw_type_error_function->define_direct_property(vm.names.length, Value(0), 0);
     m_throw_type_error_function->define_direct_property(vm.names.name, js_string(vm, ""), 0);
diff --git a/Userland/Libraries/LibJS/Runtime/NativeFunction.cpp b/Userland/Libraries/LibJS/Runtime/NativeFunction.cpp
index 1759fd22c8..ada146e147 100644
--- a/Userland/Libraries/LibJS/Runtime/NativeFunction.cpp
+++ b/Userland/Libraries/LibJS/Runtime/NativeFunction.cpp
@@ -13,7 +13,7 @@
 
 namespace JS {
 
-NativeFunction* NativeFunction::create(GlobalObject& global_object, const FlyString& name, Function<Value(VM&, GlobalObject&)> function)
+NativeFunction* NativeFunction::create(GlobalObject& global_object, const FlyString& name, Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)> function)
 {
     return global_object.heap().allocate<NativeFunction>(global_object, name, move(function), *global_object.function_prototype());
 }
@@ -28,7 +28,7 @@ NativeFunction::NativeFunction(Object& prototype)
 {
 }
 
-NativeFunction::NativeFunction(FlyString name, Function<Value(VM&, GlobalObject&)> native_function, Object& prototype)
+NativeFunction::NativeFunction(FlyString name, Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)> native_function, Object& prototype)
     : FunctionObject(prototype)
     , m_name(move(name))
     , m_native_function(move(native_function))
@@ -186,7 +186,7 @@ ThrowCompletionOr<Object*> NativeFunction::internal_construct(MarkedValueList ar
 
 Value NativeFunction::call()
 {
-    return m_native_function(vm(), global_object());
+    return TRY_OR_DISCARD(m_native_function(vm(), global_object()));
 }
 
 Value NativeFunction::construct(FunctionObject&)
diff --git a/Userland/Libraries/LibJS/Runtime/NativeFunction.h b/Userland/Libraries/LibJS/Runtime/NativeFunction.h
index d88d388ce8..05b1002d40 100644
--- a/Userland/Libraries/LibJS/Runtime/NativeFunction.h
+++ b/Userland/Libraries/LibJS/Runtime/NativeFunction.h
@@ -15,9 +15,9 @@ class NativeFunction : public FunctionObject {
     JS_OBJECT(NativeFunction, FunctionObject);
 
 public:
-    static NativeFunction* create(GlobalObject&, const FlyString& name, Function<Value(VM&, GlobalObject&)>);
+    static NativeFunction* create(GlobalObject&, const FlyString& name, Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)>);
 
-    explicit NativeFunction(FlyString name, Function<Value(VM&, GlobalObject&)>, Object& prototype);
+    explicit NativeFunction(FlyString name, Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)>, Object& prototype);
     virtual void initialize(GlobalObject&) override { }
     virtual ~NativeFunction() override;
 
@@ -42,7 +42,7 @@ private:
     virtual bool is_native_function() const final { return true; }
 
     FlyString m_name;
-    Function<Value(VM&, GlobalObject&)> m_native_function;
+    Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)> m_native_function;
     Realm* m_realm { nullptr };
 };
 
diff --git a/Userland/Libraries/LibJS/Runtime/Object.cpp b/Userland/Libraries/LibJS/Runtime/Object.cpp
index 700d93318f..dde9beb577 100644
--- a/Userland/Libraries/LibJS/Runtime/Object.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Object.cpp
@@ -952,6 +952,29 @@ void Object::set_prototype(Object* new_prototype)
 
 void Object::define_native_accessor(PropertyName const& property_name, Function<Value(VM&, GlobalObject&)> getter, Function<Value(VM&, GlobalObject&)> setter, PropertyAttributes attribute)
 {
+    Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)> completion_getter = {};
+    if (getter) {
+        completion_getter = [getter = move(getter)](auto& vm, auto& global_object) -> ThrowCompletionOr<Value> {
+            auto result = getter(vm, global_object);
+            if (auto* exception = vm.exception())
+                return throw_completion(exception->value());
+            return result;
+        };
+    }
+    Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)> completion_setter = {};
+    if (setter) {
+        completion_setter = [setter = move(setter)](auto& vm, auto& global_object) -> ThrowCompletionOr<Value> {
+            auto result = setter(vm, global_object);
+            if (auto* exception = vm.exception())
+                return throw_completion(exception->value());
+            return result;
+        };
+    }
+    define_new_native_accessor(property_name, move(completion_getter), move(completion_setter), attribute);
+}
+
+void Object::define_new_native_accessor(PropertyName const& property_name, Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)> getter, Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)> setter, PropertyAttributes attribute)
+{
     auto& vm = this->vm();
     String formatted_property_name;
     if (property_name.is_number()) {
@@ -1018,6 +1041,17 @@ Value Object::get_without_side_effects(const PropertyName& property_name) const
 
 void Object::define_native_function(PropertyName const& property_name, Function<Value(VM&, GlobalObject&)> native_function, i32 length, PropertyAttributes attribute)
 {
+    auto completion_native_function = [native_function = move(native_function), property_name](auto& vm, auto& global_object) -> ThrowCompletionOr<Value> {
+        auto result = native_function(vm, global_object);
+        if (auto* exception = vm.exception())
+            return throw_completion(exception->value());
+        return result;
+    };
+    define_new_native_function(property_name, move(completion_native_function), length, attribute);
+}
+
+void Object::define_new_native_function(PropertyName const& property_name, Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)> native_function, i32 length, PropertyAttributes attribute)
+{
     auto& vm = this->vm();
     String function_name;
     if (property_name.is_string()) {
diff --git a/Userland/Libraries/LibJS/Runtime/Object.h b/Userland/Libraries/LibJS/Runtime/Object.h
index 1e96267579..2c19851251 100644
--- a/Userland/Libraries/LibJS/Runtime/Object.h
+++ b/Userland/Libraries/LibJS/Runtime/Object.h
@@ -128,9 +128,13 @@ public:
     void define_direct_property(PropertyName const& property_name, Value value, PropertyAttributes attributes) { storage_set(property_name, { value, attributes }); };
     void define_direct_accessor(PropertyName const&, FunctionObject* getter, FunctionObject* setter, PropertyAttributes attributes);
 
+    // Legacy methods - Remove once JS_DECLARE_OLD_NATIVE_FUNCTION is removed
     void define_native_function(PropertyName const&, Function<Value(VM&, GlobalObject&)>, i32 length, PropertyAttributes attributes);
     void define_native_accessor(PropertyName const&, Function<Value(VM&, GlobalObject&)> getter, Function<Value(VM&, GlobalObject&)> setter, PropertyAttributes attributes);
 
+    void define_new_native_function(PropertyName const&, Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)>, i32 length, PropertyAttributes attributes);
+    void define_new_native_accessor(PropertyName const&, Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)> getter, Function<ThrowCompletionOr<Value>(VM&, GlobalObject&)> setter, PropertyAttributes attributes);
+
     virtual bool is_function() const { return false; }
     virtual bool is_typed_array() const { return false; }
     virtual bool is_string_object() const { return false; }
diff --git a/Userland/Libraries/LibJS/Runtime/PromiseConstructor.cpp b/Userland/Libraries/LibJS/Runtime/PromiseConstructor.cpp
index a17c4befb5..1a1829f6ea 100644
--- a/Userland/Libraries/LibJS/Runtime/PromiseConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/PromiseConstructor.cpp
@@ -72,7 +72,7 @@ static void set_iterator_record_complete(GlobalObject& global_object, Object& it
     MUST(iterator_record.set(vm.names.done, Value(true), Object::ShouldThrowExceptions::No));
 }
 
-using EndOfElementsCallback = Function<Value(PromiseValueList&)>;
+using EndOfElementsCallback = Function<ThrowCompletionOr<Value>(PromiseValueList&)>;
 using InvokeElementFunctionCallback = Function<void(PromiseValueList&, RemainingElements&, Value, size_t)>;
 
 static Value perform_promise_common(GlobalObject& global_object, Object& iterator_record, Value constructor, PromiseCapability result_capability, Value promise_resolve, EndOfElementsCallback end_of_list, InvokeElementFunctionCallback invoke_element_function)
@@ -99,7 +99,7 @@ static Value perform_promise_common(GlobalObject& global_object, Object& iterato
                 return {};
 
             if (--remaining_elements_count->value == 0)
-                return end_of_list(*values);
+                return TRY_OR_DISCARD(end_of_list(*values));
             return result_capability.promise;
         }
 
@@ -130,14 +130,12 @@ static Value perform_promise_all(GlobalObject& global_object, Object& iterator_r
 
     return perform_promise_common(
         global_object, iterator_record, constructor, result_capability, promise_resolve,
-        [&](PromiseValueList& values) -> Value {
+        [&](PromiseValueList& values) -> ThrowCompletionOr<Value> {
             auto values_array = Array::create_from(global_object, values.values());
 
-            (void)vm.call(*result_capability.resolve, js_undefined(), values_array);
-            if (vm.exception())
-                return {};
+            TRY(vm.call(*result_capability.resolve, js_undefined(), values_array));
 
-            return result_capability.promise;
+            return Value(result_capability.promise);
         },
         [&](PromiseValueList& values, RemainingElements& remaining_elements_count, Value next_promise, size_t index) {
             auto* on_fulfilled = PromiseAllResolveElementFunction::create(global_object, index, values, result_capability, remaining_elements_count);
@@ -154,14 +152,12 @@ static Value perform_promise_all_settled(GlobalObject& global_object, Object& it
 
     return perform_promise_common(
         global_object, iterator_record, constructor, result_capability, promise_resolve,
-        [&](PromiseValueList& values) -> Value {
+        [&](PromiseValueList& values) -> ThrowCompletionOr<Value> {
             auto values_array = Array::create_from(global_object, values.values());
 
-            (void)vm.call(*result_capability.resolve, js_undefined(), values_array);
-            if (vm.exception())
-                return {};
+            TRY(vm.call(*result_capability.resolve, js_undefined(), values_array));
 
-            return result_capability.promise;
+            return Value(result_capability.promise);
         },
         [&](PromiseValueList& values, RemainingElements& remaining_elements_count, Value next_promise, size_t index) {
             auto* on_fulfilled = PromiseAllSettledResolveElementFunction::create(global_object, index, values, result_capability, remaining_elements_count);
@@ -181,14 +177,14 @@ static Value perform_promise_any(GlobalObject& global_object, Object& iterator_r
 
     return perform_promise_common(
         global_object, iterator_record, constructor, result_capability, promise_resolve,
-        [&](PromiseValueList& errors) -> Value {
+        [&](PromiseValueList& errors) -> ThrowCompletionOr<Value> {
             auto errors_array = Array::create_from(global_object, errors.values());
 
             auto* error = AggregateError::create(global_object);
             MUST(error->define_property_or_throw(vm.names.errors, { .value = errors_array, .writable = true, .enumerable = false, .configurable = true }));
 
             vm.throw_exception(global_object, error);
-            return {};
+            return throw_completion(error);
         },
         [&](PromiseValueList& errors, RemainingElements& remaining_elements_count, Value next_promise, size_t index) {
             auto* on_rejected = PromiseAnyRejectElementFunction::create(global_object, index, errors, result_capability, remaining_elements_count);
@@ -205,8 +201,8 @@ static Value perform_promise_race(GlobalObject& global_object, Object& iterator_
 
     return perform_promise_common(
         global_object, iterator_record, constructor, result_capability, promise_resolve,
-        [&](PromiseValueList&) -> Value {
-            return result_capability.promise;
+        [&](PromiseValueList&) -> ThrowCompletionOr<Value> {
+            return Value(result_capability.promise);
         },
         [&](PromiseValueList&, RemainingElements&, Value next_promise, size_t) {
             (void)next_promise.invoke(global_object, vm.names.then, result_capability.resolve, result_capability.reject);
diff --git a/Userland/Libraries/LibJS/Runtime/PromisePrototype.cpp b/Userland/Libraries/LibJS/Runtime/PromisePrototype.cpp
index 711add5389..1dac15c036 100644
--- a/Userland/Libraries/LibJS/Runtime/PromisePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/PromisePrototype.cpp
@@ -69,35 +69,35 @@ JS_DEFINE_OLD_NATIVE_FUNCTION(PromisePrototype::finally)
         catch_finally = on_finally;
     } else {
         // 27.2.5.3.1 Then Finally Functions, https://tc39.es/ecma262/#sec-thenfinallyfunctions
-        auto* then_finally_function = NativeFunction::create(global_object, "", [constructor_handle = make_handle(constructor), on_finally_handle = make_handle(&on_finally.as_function())](auto& vm, auto& global_object) -> Value {
+        auto* then_finally_function = NativeFunction::create(global_object, "", [constructor_handle = make_handle(constructor), on_finally_handle = make_handle(&on_finally.as_function())](auto& vm, auto& global_object) -> ThrowCompletionOr<Value> {
             auto& constructor = const_cast<FunctionObject&>(*constructor_handle.cell());
             auto& on_finally = const_cast<FunctionObject&>(*on_finally_handle.cell());
             auto value = vm.argument(0);
-            auto result = TRY_OR_DISCARD(vm.call(on_finally, js_undefined()));
+            auto result = TRY(vm.call(on_finally, js_undefined()));
             auto* promise = promise_resolve(global_object, constructor, result);
-            if (vm.exception())
-                return {};
-            auto* value_thunk = NativeFunction::create(global_object, "", [value](auto&, auto&) -> Value {
+            if (auto* exception = vm.exception())
+                return throw_completion(exception->value());
+            auto* value_thunk = NativeFunction::create(global_object, "", [value](auto&, auto&) -> ThrowCompletionOr<Value> {
                 return value;
             });
-            return TRY_OR_DISCARD(Value(promise).invoke(global_object, vm.names.then, value_thunk));
+            return TRY(Value(promise).invoke(global_object, vm.names.then, value_thunk));
         });
         then_finally_function->define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
 
         // 27.2.5.3.2 Catch Finally Functions, https://tc39.es/ecma262/#sec-catchfinallyfunctions
-        auto* catch_finally_function = NativeFunction::create(global_object, "", [constructor_handle = make_handle(constructor), on_finally_handle = make_handle(&on_finally.as_function())](auto& vm, auto& global_object) -> Value {
+        auto* catch_finally_function = NativeFunction::create(global_object, "", [constructor_handle = make_handle(constructor), on_finally_handle = make_handle(&on_finally.as_function())](auto& vm, auto& global_object) -> ThrowCompletionOr<Value> {
             auto& constructor = const_cast<FunctionObject&>(*constructor_handle.cell());
             auto& on_finally = const_cast<FunctionObject&>(*on_finally_handle.cell());
             auto reason = vm.argument(0);
-            auto result = TRY_OR_DISCARD(vm.call(on_finally, js_undefined()));
+            auto result = TRY(vm.call(on_finally, js_undefined()));
             auto* promise = promise_resolve(global_object, constructor, result);
-            if (vm.exception())
-                return {};
-            auto* thrower = NativeFunction::create(global_object, "", [reason](auto& vm, auto& global_object) -> Value {
+            if (auto* exception = vm.exception())
+                return throw_completion(exception->value());
+            auto* thrower = NativeFunction::create(global_object, "", [reason](auto& vm, auto& global_object) -> ThrowCompletionOr<Value> {
                 vm.throw_exception(global_object, reason);
-                return {};
+                return throw_completion(reason);
             });
-            return TRY_OR_DISCARD(Value(promise).invoke(global_object, vm.names.then, thrower));
+            return TRY(Value(promise).invoke(global_object, vm.names.then, thrower));
         });
         catch_finally_function->define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
 
diff --git a/Userland/Libraries/LibJS/Runtime/PromiseReaction.cpp b/Userland/Libraries/LibJS/Runtime/PromiseReaction.cpp
index ac5729011d..c7fd18af34 100644
--- a/Userland/Libraries/LibJS/Runtime/PromiseReaction.cpp
+++ b/Userland/Libraries/LibJS/Runtime/PromiseReaction.cpp
@@ -26,17 +26,15 @@ PromiseCapability new_promise_capability(GlobalObject& global_object, Value cons
     } promise_capability_functions;
 
     // 27.2.1.5.1 GetCapabilitiesExecutor Functions, https://tc39.es/ecma262/#sec-getcapabilitiesexecutor-functions
-    auto* executor = NativeFunction::create(global_object, "", [&promise_capability_functions](auto& vm, auto& global_object) -> Value {
+    auto* executor = NativeFunction::create(global_object, "", [&promise_capability_functions](auto& vm, auto& global_object) -> ThrowCompletionOr<Value> {
         auto resolve = vm.argument(0);
         auto reject = vm.argument(1);
         // No idea what other engines say here.
         if (!promise_capability_functions.resolve.is_undefined()) {
-            vm.template throw_exception<TypeError>(global_object, ErrorType::GetCapabilitiesExecutorCalledMultipleTimes);
-            return {};
+            return vm.template throw_completion<TypeError>(global_object, ErrorType::GetCapabilitiesExecutorCalledMultipleTimes);
         }
         if (!promise_capability_functions.reject.is_undefined()) {
-            vm.template throw_exception<TypeError>(global_object, ErrorType::GetCapabilitiesExecutorCalledMultipleTimes);
-            return {};
+            return vm.template throw_completion<TypeError>(global_object, ErrorType::GetCapabilitiesExecutorCalledMultipleTimes);
         }
         promise_capability_functions.resolve = resolve;
         promise_capability_functions.reject = reject;
diff --git a/Userland/Libraries/LibJS/Runtime/PromiseResolvingFunction.cpp b/Userland/Libraries/LibJS/Runtime/PromiseResolvingFunction.cpp
index e6553c92c9..87264a9c1a 100644
--- a/Userland/Libraries/LibJS/Runtime/PromiseResolvingFunction.cpp
+++ b/Userland/Libraries/LibJS/Runtime/PromiseResolvingFunction.cpp
@@ -32,7 +32,7 @@ void PromiseResolvingFunction::initialize(GlobalObject& global_object)
 
 Value PromiseResolvingFunction::call()
 {
-    return m_native_function(vm(), global_object(), m_promise, m_already_resolved);
+    return TRY_OR_DISCARD(m_native_function(vm(), global_object(), m_promise, m_already_resolved));
 }
 
 void PromiseResolvingFunction::visit_edges(Cell::Visitor& visitor)
diff --git a/Userland/Libraries/LibJS/Runtime/PromiseResolvingFunction.h b/Userland/Libraries/LibJS/Runtime/PromiseResolvingFunction.h
index f15fc6efea..ceb11e7315 100644
--- a/Userland/Libraries/LibJS/Runtime/PromiseResolvingFunction.h
+++ b/Userland/Libraries/LibJS/Runtime/PromiseResolvingFunction.h
@@ -25,7 +25,7 @@ class PromiseResolvingFunction final : public NativeFunction {
     JS_OBJECT(PromiseResolvingFunction, NativeFunction);
 
 public:
-    using FunctionType = Function<Value(VM&, GlobalObject&, Promise&, AlreadyResolved&)>;
+    using FunctionType = Function<ThrowCompletionOr<Value>(VM&, GlobalObject&, Promise&, AlreadyResolved&)>;
 
     static PromiseResolvingFunction* create(GlobalObject&, Promise&, AlreadyResolved&, FunctionType);
 
diff --git a/Userland/Libraries/LibJS/Runtime/ProxyConstructor.cpp b/Userland/Libraries/LibJS/Runtime/ProxyConstructor.cpp
index e2a3e25aac..ada40fab71 100644
--- a/Userland/Libraries/LibJS/Runtime/ProxyConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ProxyConstructor.cpp
@@ -70,7 +70,7 @@ JS_DEFINE_OLD_NATIVE_FUNCTION(ProxyConstructor::revocable)
         return {};
 
     // 28.2.2.1.1 Proxy Revocation Functions, https://tc39.es/ecma262/#sec-proxy-revocation-functions
-    auto* revoker = NativeFunction::create(global_object, "", [proxy_handle = make_handle(proxy)](auto&, auto&) -> Value {
+    auto* revoker = NativeFunction::create(global_object, "", [proxy_handle = make_handle(proxy)](auto&, auto&) -> ThrowCompletionOr<Value> {
         auto& proxy = const_cast<ProxyObject&>(*proxy_handle.cell());
         if (proxy.is_revoked())
             return js_undefined();
diff --git a/Userland/Libraries/LibJS/Runtime/ShadowRealm.cpp b/Userland/Libraries/LibJS/Runtime/ShadowRealm.cpp
index c9369ae74f..02ec8a3ab5 100644
--- a/Userland/Libraries/LibJS/Runtime/ShadowRealm.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ShadowRealm.cpp
@@ -184,11 +184,11 @@ ThrowCompletionOr<Value> shadow_realm_import_value(GlobalObject& global_object,
 
     // FinishDynamicImport, 5. Perform ! PerformPromiseThen(innerPromise, onFulfilled, onRejected).
     promise->perform_then(
-        NativeFunction::create(global_object, "", [](auto&, auto&) -> Value {
+        NativeFunction::create(global_object, "", [](auto&, auto&) -> ThrowCompletionOr<Value> {
             // Not called because we hardcoded a rejection above.
             TODO();
         }),
-        NativeFunction::create(global_object, "", [reject = make_handle(inner_capability.reject)](auto& vm, auto& global_object) -> Value {
+        NativeFunction::create(global_object, "", [reject = make_handle(inner_capability.reject)](auto& vm, auto& global_object) -> ThrowCompletionOr<Value> {
             auto error = vm.argument(0);
 
             // a. Perform ! Call(promiseCapability.[[Reject]], undefined, « error »).
@@ -214,7 +214,7 @@ ThrowCompletionOr<Value> shadow_realm_import_value(GlobalObject& global_object,
     auto* on_fulfilled = NativeFunction::create(
         global_object,
         "",
-        [string = move(export_name_string)](auto& vm, auto& global_object) -> Value {
+        [string = move(export_name_string)](auto& vm, auto& global_object) -> ThrowCompletionOr<Value> {
             // 1. Assert: exports is a module namespace exotic object.
             auto& exports = vm.argument(0).as_object();
 
@@ -225,23 +225,21 @@ ThrowCompletionOr<Value> shadow_realm_import_value(GlobalObject& global_object,
             // 4. Assert: Type(string) is String.
 
             // 5. Let hasOwn be ? HasOwnProperty(exports, string).
-            auto has_own = TRY_OR_DISCARD(exports.has_own_property(string));
+            auto has_own = TRY(exports.has_own_property(string));
 
             // 6. If hasOwn is false, throw a TypeError exception.
-            if (!has_own) {
-                vm.template throw_exception<TypeError>(global_object, ErrorType::MissingRequiredProperty, string);
-                return {};
-            }
+            if (!has_own)
+                return vm.template throw_completion<TypeError>(global_object, ErrorType::MissingRequiredProperty, string);
 
             // 7. Let value be ? Get(exports, string).
-            auto value = TRY_OR_DISCARD(exports.get(string));
+            auto value = TRY(exports.get(string));
 
             // 8. Let realm be f.[[Realm]].
             auto* realm = function->realm();
             VERIFY(realm);
 
             // 9. Return ? GetWrappedValue(realm, value).
-            return TRY_OR_DISCARD(get_wrapped_value(global_object, *realm, value));
+            return get_wrapped_value(global_object, *realm, value);
         });
     on_fulfilled->define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
     on_fulfilled->define_direct_property(vm.names.name, js_string(vm, String::empty()), Attribute::Configurable);
@@ -252,9 +250,8 @@ ThrowCompletionOr<Value> shadow_realm_import_value(GlobalObject& global_object,
 
     // NOTE: Even though the spec tells us to use %ThrowTypeError%, it's not observable if we actually do.
     // Throw a nicer TypeError forwarding the import error message instead (we know the argument is an Error object).
-    auto* throw_type_error = NativeFunction::create(global_object, {}, [](auto& vm, auto& global_object) -> Value {
-        vm.template throw_exception<TypeError>(global_object, vm.argument(0).as_object().get_without_side_effects(vm.names.message).as_string().string());
-        return {};
+    auto* throw_type_error = NativeFunction::create(global_object, {}, [](auto& vm, auto& global_object) -> ThrowCompletionOr<Value> {
+        return vm.template throw_completion<TypeError>(global_object, vm.argument(0).as_object().get_without_side_effects(vm.names.message).as_string().string());
     });
 
     // 17. Return ! PerformPromiseThen(innerCapability.[[Promise]], onFulfilled, callerRealm.[[Intrinsics]].[[%ThrowTypeError%]], promiseCapability).
diff --git a/Userland/Libraries/LibWeb/WebAssembly/WebAssemblyObject.cpp b/Userland/Libraries/LibWeb/WebAssembly/WebAssemblyObject.cpp
index 1c4b72c4c2..de5ed754e7 100644
--- a/Userland/Libraries/LibWeb/WebAssembly/WebAssemblyObject.cpp
+++ b/Userland/Libraries/LibWeb/WebAssembly/WebAssemblyObject.cpp
@@ -442,7 +442,7 @@ JS::NativeFunction* create_native_function(Wasm::FunctionAddress address, String
     auto function = JS::NativeFunction::create(
         global_object,
         name,
-        [address, type = type.release_value()](JS::VM& vm, JS::GlobalObject& global_object) -> JS::Value {
+        [address, type = type.release_value()](JS::VM& vm, JS::GlobalObject& global_object) -> JS::ThrowCompletionOr<JS::Value> {
             Vector<Wasm::Value> values;
             values.ensure_capacity(type.parameters().size());
 
@@ -453,15 +453,13 @@ JS::NativeFunction* create_native_function(Wasm::FunctionAddress address, String
                 if (result.has_value())
                     values.append(result.release_value());
                 else
-                    return {};
+                    return JS::throw_completion(vm.exception()->value());
             }
 
             auto result = WebAssemblyObject::s_abstract_machine.invoke(address, move(values));
             // FIXME: Use the convoluted mapping of errors defined in the spec.
-            if (result.is_trap()) {
-                vm.throw_exception<JS::TypeError>(global_object, String::formatted("Wasm execution trapped (WIP): {}", result.trap().reason));
-                return {};
-            }
+            if (result.is_trap())
+                return vm.throw_completion<JS::TypeError>(global_object, String::formatted("Wasm execution trapped (WIP): {}", result.trap().reason));
 
             if (result.values().is_empty())
                 return JS::js_undefined();
@@ -473,7 +471,7 @@ JS::NativeFunction* create_native_function(Wasm::FunctionAddress address, String
             for (auto& entry : result.values())
                 result_values.append(to_js_value(entry, global_object));
 
-            return JS::Array::create_from(global_object, result_values);
+            return JS::Value(JS::Array::create_from(global_object, result_values));
         });
 
     WebAssemblyObject::s_global_cache.function_instances.set(address, function);