simplify setUpdateListener example

Author: WofWca

src-docs/spec/setUpdateListener.md

@@ -32,43 +32,28 @@ Each `update` which is passed to the callback comes with the following propertie
 Example:
 
 ```js
-let myDocumentState = localStorage.getItem("myDocumentState") ?? "";
-
-let initialPendingUpdatesHandled = false;
+let myDocumentState = "";
 const initialPendingUpdatesHandledPromise = window.webxdc.setUpdateListener(
   (update) => {
     // Remember that the listener is invoked for
     // your own `window.webxdc.sendUpdate()` calls as well!
 
-    applyDocumentUpdate(update.payload);
-    localStorage.setItem("myDocumentState", myDocumentState);
-    localStorage.setItem("lastHandledUpdateSerial", update.serial);
+    // Dummy document update logic.
+    // Yours might be more complex,
+    // such as applying a chess move to the board.
+    myDocumentState = myDocumentUpdate;
 
     const areMoreUpdatesPending = update.serial !== update.max_serial;
-    if (
-      !areMoreUpdatesPending &&
-      // We'll make the initial render when the promise resolves,
-      // because if there are no pending updates,
-      // the listener will not be invoked.
-      initialPendingUpdatesHandled
-    ) {
+    if (!areMoreUpdatesPending) {
       renderDocument();
     }
-  },
-  parseInt(localStorage.getItem("lastHandledUpdateSerial") ?? "0")
+  }
 );
 
 initialPendingUpdatesHandledPromise.then(() => {
-  initialPendingUpdatesHandled = true;
   renderDocument();
 });
 
-function applyDocumentUpdate(myDocumentUpdate) {
-  // Dummy `applyDocumentUpdate` logic.
-  // Yours might be more complex,
-  // such as applying a chess move to the board.
-  myDocumentState = myDocumentUpdate;
-}
 // Let's only call this when there are no pending updates.
 function renderDocument() {
   document.body.innerText = myDocumentState;