LibWeb: Stub out a basic IntersectionObserver interface

Note there are a couple of type differences between the spec and the IDL
file added in this commit. For example, we will need to support a type
of Variant to handle spec types such as "(double or sequence<double>)".
But for now, this allows web pages to construct an IntersectionObserver
with any valid type.

Userland/Libraries/LibWeb/Bindings/WindowObjectHelper.h

@@ -207,6 +207,8 @@
 #include <LibWeb/Bindings/ImageConstructor.h>
 #include <LibWeb/Bindings/ImageDataConstructor.h>
 #include <LibWeb/Bindings/ImageDataPrototype.h>
+#include <LibWeb/Bindings/IntersectionObserverConstructor.h>
+#include <LibWeb/Bindings/IntersectionObserverPrototype.h>
 #include <LibWeb/Bindings/MediaQueryListConstructor.h>
 #include <LibWeb/Bindings/MediaQueryListEventConstructor.h>
 #include <LibWeb/Bindings/MediaQueryListEventPrototype.h>
@@ -386,6 +388,7 @@
     ADD_WINDOW_OBJECT_INTERFACE(HTMLUnknownElement)        \
     ADD_WINDOW_OBJECT_INTERFACE(HTMLVideoElement)          \
     ADD_WINDOW_OBJECT_INTERFACE(ImageData)                 \
+    ADD_WINDOW_OBJECT_INTERFACE(IntersectionObserver)      \
     ADD_WINDOW_OBJECT_INTERFACE(MediaQueryList)            \
     ADD_WINDOW_OBJECT_INTERFACE(MediaQueryListEvent)       \
     ADD_WINDOW_OBJECT_INTERFACE(MessageChannel)            \

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -188,7 +188,8 @@ set(SOURCES
     HTML/WebSocket.cpp
     HighResolutionTime/Performance.cpp
     InProcessWebView.cpp
-        Layout/BlockContainer.cpp
+    IntersectionObserver/IntersectionObserver.cpp
+    Layout/BlockContainer.cpp
     Layout/BlockFormattingContext.cpp
     Layout/Box.cpp
     Layout/BoxModelMetrics.cpp
@@ -472,6 +473,7 @@ libweb_js_wrapper(HTML/PromiseRejectionEvent)
 libweb_js_wrapper(HTML/SubmitEvent)
 libweb_js_wrapper(HTML/WebSocket)
 libweb_js_wrapper(HighResolutionTime/Performance)
+libweb_js_wrapper(IntersectionObserver/IntersectionObserver)
 libweb_js_wrapper(NavigationTiming/PerformanceTiming)
 libweb_js_wrapper(RequestIdleCallback/IdleDeadline)
 libweb_js_wrapper(ResizeObserver/ResizeObserver)

Userland/Libraries/LibWeb/Forward.h

@@ -204,6 +204,10 @@ namespace Web::HighResolutionTime {
 class Performance;
 }
 
+namespace Web::IntersectionObserver {
+class IntersectionObserver;
+}
+
 namespace Web::NavigationTiming {
 class PerformanceTiming;
 }
@@ -386,6 +390,7 @@ class HTMLUnknownElementWrapper;
 class HTMLVideoElementWrapper;
 class IdleDeadlineWrapper;
 class ImageDataWrapper;
+class IntersectionObserverWrapper;
 class KeyboardEventWrapper;
 class LocationObject;
 class MediaQueryListWrapper;

Userland/Libraries/LibWeb/IntersectionObserver/IntersectionObserver.cpp

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2021, Tim Flynn <trflynn89@pm.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/DOM/Element.h>
+#include <LibWeb/IntersectionObserver/IntersectionObserver.h>
+
+namespace Web::IntersectionObserver {
+
+// https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-intersectionobserver
+NonnullRefPtr<IntersectionObserver> IntersectionObserver::create_with_global_object(JS::GlobalObject& global_object, JS::Value callback, IntersectionObserverInit const& options)
+{
+    // FIXME: Implement
+    (void)global_object;
+    (void)callback;
+    (void)options;
+
+    return adopt_ref(*new IntersectionObserver);
+}
+
+// https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-observe
+void IntersectionObserver::observe(DOM::Element& target)
+{
+    // FIXME: Implement
+    (void)target;
+}
+
+// https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-unobserve
+void IntersectionObserver::unobserve(DOM::Element& target)
+{
+    // FIXME: Implement
+    (void)target;
+}
+
+// https://w3c.github.io/IntersectionObserver/#dom-intersectionobserver-disconnect
+void IntersectionObserver::disconnect()
+{
+    // FIXME: Implement
+}
+
+}

Userland/Libraries/LibWeb/IntersectionObserver/IntersectionObserver.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2021, Tim Flynn <trflynn89@pm.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/NonnullRefPtr.h>
+#include <AK/RefCounted.h>
+#include <LibWeb/Bindings/Wrappable.h>
+
+namespace Web::IntersectionObserver {
+
+struct IntersectionObserverInit {
+    DOM::Node* root { nullptr };
+    String root_margin { "0px"sv };
+    JS::Value threshold { 0 };
+};
+
+// https://w3c.github.io/IntersectionObserver/#intersection-observer-interface
+class IntersectionObserver
+    : public RefCounted<IntersectionObserver>
+    , public Bindings::Wrappable {
+public:
+    using WrapperType = Bindings::IntersectionObserverWrapper;
+
+    static NonnullRefPtr<IntersectionObserver> create_with_global_object(JS::GlobalObject&, JS::Value callback, IntersectionObserverInit const& options = {});
+
+    void observe(DOM::Element& target);
+    void unobserve(DOM::Element& target);
+    void disconnect();
+};
+
+}

Userland/Libraries/LibWeb/IntersectionObserver/IntersectionObserver.idl

@@ -0,0 +1,22 @@
+[Exposed=(Window)]
+interface IntersectionObserver {
+    // FIXME: Should be: IntersectionObserverCallback
+    constructor(any callback, optional IntersectionObserverInit options = {});
+
+    undefined observe(Element target);
+    undefined unobserve(Element target);
+    undefined disconnect();
+
+    // FIXME:
+    // sequence<IntersectionObserverEntry> takeRecords();
+};
+
+dictionary IntersectionObserverInit {
+    // FIXME: Should be: (Element or Document)?
+    Node? root = null;
+
+    DOMString rootMargin = "0px";
+
+    // FIXME: Should be: (double or sequence<double>)
+    any threshold = 0;
+};