Tools for awaiting ready -- still can't make focus() work

ts/event.ts

@@ -0,0 +1,16 @@
+export function waitForEvent(target: EventTarget, eventType: string) {
+    return new Promise((resolve) => {
+        function handler(event: Event) {
+            target.removeEventListener(eventType, handler);
+            resolve(event);
+        }
+
+        target.addEventListener(eventType, handler);
+    });
+}
+
+export function waitForAnimationFrame() {
+    return new Promise((resolve) => {
+        requestAnimationFrame(resolve);
+    });
+}