LibWeb/WebIDL: Introduce ObservableArray

ObservableArray inherits from JS::Array and overrides `internal_set`
and `internal_delete` to run an interceptor callback when an indexed
item is added or deleted.

Userland/Libraries/LibJS/Runtime/Array.h

@@ -44,7 +44,7 @@ public:
 
     virtual ThrowCompletionOr<Optional<PropertyDescriptor>> internal_get_own_property(PropertyKey const&) const override final;
     virtual ThrowCompletionOr<bool> internal_define_own_property(PropertyKey const&, PropertyDescriptor const&) override final;
-    virtual ThrowCompletionOr<bool> internal_delete(PropertyKey const&) override final;
+    virtual ThrowCompletionOr<bool> internal_delete(PropertyKey const&) override;
     virtual ThrowCompletionOr<MarkedVector<Value>> internal_own_property_keys() const override final;
 
     [[nodiscard]] bool length_is_writable() const { return m_length_writable; }

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -647,6 +647,7 @@ set(SOURCES
     WebIDL/Buffers.cpp
     WebIDL/CallbackType.cpp
     WebIDL/DOMException.cpp
+    WebIDL/ObservableArray.cpp
     WebIDL/OverloadResolution.cpp
     WebIDL/Promise.cpp
     WebSockets/WebSocket.cpp

Userland/Libraries/LibWeb/WebIDL/ObservableArray.cpp

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2024, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Bindings/ExceptionOrUtils.h>
+#include <LibWeb/WebIDL/ObservableArray.h>
+
+namespace Web::WebIDL {
+
+JS::NonnullGCPtr<ObservableArray> ObservableArray::create(JS::Realm& realm)
+{
+    auto prototype = realm.intrinsics().array_prototype();
+    return realm.heap().allocate<ObservableArray>(realm, prototype);
+}
+
+ObservableArray::ObservableArray(Object& prototype)
+    : JS::Array(prototype)
+{
+}
+
+void ObservableArray::visit_edges(JS::Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    visitor.visit(m_on_set_an_indexed_value);
+    visitor.visit(m_on_delete_an_indexed_value);
+}
+
+void ObservableArray::set_on_set_an_indexed_value_callback(SetAnIndexedValueCallbackFunction&& callback)
+{
+    m_on_set_an_indexed_value = create_heap_function(heap(), move(callback));
+}
+
+void ObservableArray::set_on_delete_an_indexed_value_callback(DeleteAnIndexedValueCallbackFunction&& callback)
+{
+    m_on_delete_an_indexed_value = create_heap_function(heap(), move(callback));
+}
+
+JS::ThrowCompletionOr<bool> ObservableArray::internal_set(JS::PropertyKey const& property_key, JS::Value value, JS::Value receiver, JS::CacheablePropertyMetadata* metadata)
+{
+    if (property_key.is_number() && m_on_set_an_indexed_value)
+        TRY(Bindings::throw_dom_exception_if_needed(vm(), [&] { return m_on_set_an_indexed_value->function()(value); }));
+    return TRY(Base::internal_set(property_key, value, receiver, metadata));
+}
+
+JS::ThrowCompletionOr<bool> ObservableArray::internal_delete(JS::PropertyKey const& property_key)
+{
+    if (property_key.is_number() && m_on_delete_an_indexed_value)
+        TRY(Bindings::throw_dom_exception_if_needed(vm(), [&] { return m_on_delete_an_indexed_value->function()(); }));
+    return JS::Array::internal_delete(property_key);
+}
+
+JS::ThrowCompletionOr<void> ObservableArray::append(JS::Value value)
+{
+    if (m_on_set_an_indexed_value)
+        TRY(Bindings::throw_dom_exception_if_needed(vm(), [&] { return m_on_set_an_indexed_value->function()(value); }));
+    indexed_properties().append(value);
+    return {};
+}
+
+void ObservableArray::clear()
+{
+    while (!indexed_properties().is_empty()) {
+        indexed_properties().storage()->take_first();
+    }
+}
+
+}

Userland/Libraries/LibWeb/WebIDL/ObservableArray.h

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2024, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/Array.h>
+#include <LibWeb/WebIDL/ExceptionOr.h>
+
+namespace Web::WebIDL {
+
+// https://webidl.spec.whatwg.org/#idl-observable-array
+class ObservableArray final : public JS::Array {
+public:
+    static JS::NonnullGCPtr<ObservableArray> create(JS::Realm& realm);
+
+    virtual JS::ThrowCompletionOr<bool> internal_set(JS::PropertyKey const& property_key, JS::Value value, JS::Value receiver, JS::CacheablePropertyMetadata* metadata = nullptr) override;
+    virtual JS::ThrowCompletionOr<bool> internal_delete(JS::PropertyKey const& property_key) override;
+
+    using SetAnIndexedValueCallbackFunction = Function<ExceptionOr<void>(JS::Value&)>;
+    using DeleteAnIndexedValueCallbackFunction = Function<ExceptionOr<void>()>;
+
+    void set_on_set_an_indexed_value_callback(SetAnIndexedValueCallbackFunction&& callback);
+    void set_on_delete_an_indexed_value_callback(DeleteAnIndexedValueCallbackFunction&& callback);
+
+    JS::ThrowCompletionOr<void> append(JS::Value value);
+    void clear();
+
+    explicit ObservableArray(Object& prototype);
+
+    virtual void visit_edges(JS::Cell::Visitor&) override;
+
+private:
+    using SetAnIndexedValueCallbackHeapFunction = JS::HeapFunction<SetAnIndexedValueCallbackFunction::FunctionType>;
+    using DeleteAnIndexedValueCallbackHeapFunction = JS::HeapFunction<DeleteAnIndexedValueCallbackFunction::FunctionType>;
+
+    JS::GCPtr<SetAnIndexedValueCallbackHeapFunction> m_on_set_an_indexed_value;
+    JS::GCPtr<DeleteAnIndexedValueCallbackHeapFunction> m_on_delete_an_indexed_value;
+};
+
+}