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

ts/slelem.ts

@@ -1,10 +1,18 @@
 import { ElemWrapper } from "./elemwrapper";
 
+interface SLBaseElem extends HTMLElement {
+    updateComplete: Promise<void>;
+}
+
 export class SLElem extends ElemWrapper {
     constructor(tagName: string) {
         super(document.createElement(tagName));
     }
 
+    public async awaitUpdate() {
+        await (this.elem as SLBaseElem).updateComplete;
+    }
+
     public setSlot(slot: string) {
         this.setAttribute("slot", slot);
     }