LibWeb: Implement window.event as a [Replaceable] property

This is the result of debugging React DOM, which would throw a TypeError
when assigning to window.event in strict mode and then not complete
rendering - here:
https://github.com/facebook/react/blob/cae6350/packages/shared/invokeGuardedCallbackImpl.js#L134

With this change, the following minimal React example now works!

    <div id="app"></div>
    <script src="react.development.js"></script>
    <script src="react-dom.development.js"></script>
    <script>
        ReactDOM.render(
            React.createElement("h1", null, "Hello World"),
            document.getElementById("app")
        );
    </script>

2 files changed, 8 insertions, 1 deletions

diff --git a/Userland/Libraries/LibWeb/Bindings/WindowObject.cpp b/Userland/Libraries/LibWeb/Bindings/WindowObject.cpp
index 1f9b174e1b..989db89812 100644
--- a/Userland/Libraries/LibWeb/Bindings/WindowObject.cpp
+++ b/Userland/Libraries/LibWeb/Bindings/WindowObject.cpp
@@ -24,6 +24,7 @@
 #include <LibWeb/Bindings/NavigatorObject.h>
 #include <LibWeb/Bindings/NodeWrapperFactory.h>
 #include <LibWeb/Bindings/PerformanceWrapper.h>
+#include <LibWeb/Bindings/Replaceable.h>
 #include <LibWeb/Bindings/ScreenWrapper.h>
 #include <LibWeb/Bindings/WindowObject.h>
 #include <LibWeb/DOM/Document.h>
@@ -89,7 +90,7 @@ void WindowObject::initialize_global_object()
     define_native_function("scrollBy", scroll_by, 2, attr);
 
     // Legacy
-    define_native_accessor("event", event_getter, {}, JS::Attribute::Enumerable);
+    define_native_accessor("event", event_getter, event_setter, JS::Attribute::Enumerable);
 
     define_direct_property("navigator", heap().allocate<NavigatorObject>(*this, *this), JS::Attribute::Enumerable | JS::Attribute::Configurable);
     define_direct_property("location", heap().allocate<LocationObject>(*this, *this), JS::Attribute::Enumerable | JS::Attribute::Configurable);
@@ -439,6 +440,11 @@ JS_DEFINE_NATIVE_FUNCTION(WindowObject::event_getter)
     return wrap(global_object, const_cast<DOM::Event&>(*impl->current_event()));
 }
 
+JS_DEFINE_NATIVE_FUNCTION(WindowObject::event_setter)
+{
+    REPLACEABLE_PROPERTY_SETTER(WindowObject, event);
+}
+
 JS_DEFINE_NATIVE_FUNCTION(WindowObject::inner_width_getter)
 {
     auto* impl = impl_from(vm, global_object);
diff --git a/Userland/Libraries/LibWeb/Bindings/WindowObject.h b/Userland/Libraries/LibWeb/Bindings/WindowObject.h
index d574546740..7a5f014980 100644
--- a/Userland/Libraries/LibWeb/Bindings/WindowObject.h
+++ b/Userland/Libraries/LibWeb/Bindings/WindowObject.h
@@ -68,6 +68,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(screen_getter);
 
     JS_DECLARE_NATIVE_FUNCTION(event_getter);
+    JS_DECLARE_NATIVE_FUNCTION(event_setter);
 
     JS_DECLARE_NATIVE_FUNCTION(inner_width_getter);
     JS_DECLARE_NATIVE_FUNCTION(inner_height_getter);