Protect editor sessions from unsaved link navigation and unload

packages/block-editor/src/index.ts

@@ -1,2 +1,3 @@
 export * from "./state.ts";
 export * from "./runtime.ts";
+export * from "./unsaved.ts";

packages/block-editor/src/unsaved.ts

@@ -0,0 +1,40 @@
+export function mountUnsavedChangesGuard(
+  root: HTMLElement,
+  options: { hasUnsavedChanges(): boolean; confirmLeave(): boolean },
+): { destroy(): void } {
+  const document = root.ownerDocument;
+  const view = document.defaultView!;
+  let destroyed = false;
+  const dirty = () => !destroyed && root.isConnected && options.hasUnsavedChanges();
+  const beforeUnload = (event: BeforeUnloadEvent) => {
+    if (!dirty()) return;
+    event.preventDefault();
+    event.returnValue = "";
+  };
+  const click = (event: MouseEvent) => {
+    if (event.defaultPrevented || event.button !== 0 || event.ctrlKey || event.metaKey || event.shiftKey || event.altKey) return;
+    const target = event.target as Element | null;
+    const link = target?.closest?.("a[href]") as HTMLAnchorElement | null;
+    if (!link || link.hasAttribute("download") || (link.target && link.target !== "_self")) return;
+    const url = new URL(link.href, document.baseURI);
+    if (!["http:", "https:"].includes(url.protocol)) return;
+    const current = new URL(view.location.href);
+    if (url.origin === current.origin && url.pathname === current.pathname && url.search === current.search && url.hash) return;
+    if (dirty() && !options.confirmLeave()) {
+      event.preventDefault();
+      event.stopImmediatePropagation();
+    }
+  };
+  const observer = new view.MutationObserver(() => { if (!root.isConnected) destroy(); });
+  function destroy() {
+    if (destroyed) return;
+    destroyed = true;
+    view.removeEventListener("beforeunload", beforeUnload);
+    document.removeEventListener("click", click, true);
+    observer.disconnect();
+  }
+  view.addEventListener("beforeunload", beforeUnload);
+  document.addEventListener("click", click, true);
+  observer.observe(document.documentElement, { childList: true, subtree: true });
+  return { destroy };
+}