Bug 1409976 - Add `slotchange` event

* Add support for `slotchange` event
* Signal `slotchange` when slot's assigned nodes changes

Tag #1375

1 files changed, 21 insertions, 0 deletions

diff --git a/dom/base/DocGroup.cpp b/dom/base/DocGroup.cpp
index 30c058f0c..826a71812 100644
--- a/dom/base/DocGroup.cpp
+++ b/dom/base/DocGroup.cpp
@@ -6,10 +6,13 @@
 #include "mozilla/StaticPtr.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "nsIDocShell.h"
+#include "nsDOMMutationObserver.h"
 
 namespace mozilla {
 namespace dom {
 
+AutoTArray<RefPtr<DocGroup>, 2>* DocGroup::sPendingDocGroups = nullptr;
+
 /* static */ void
 DocGroup::GetKey(nsIPrincipal* aPrincipal, nsACString& aKey)
 {
@@ -54,5 +57,23 @@ DocGroup::~DocGroup()
 
 NS_IMPL_ISUPPORTS(DocGroup, nsISupports)
 
+void
+DocGroup::SignalSlotChange(const HTMLSlotElement* aSlot)
+{
+  if (mSignalSlotList.Contains(aSlot)) {
+    return;
+  }
+
+  mSignalSlotList.AppendElement(const_cast<HTMLSlotElement*>(aSlot));
+
+  if (!sPendingDocGroups) {
+    // Queue a mutation observer compound microtask.
+    nsDOMMutationObserver::QueueMutationObserverMicroTask();
+    sPendingDocGroups = new AutoTArray<RefPtr<DocGroup>, 2>;
+  }
+
+  sPendingDocGroups->AppendElement(this);
+}
+
 }
 }