refactor: simplify bootstrap (#190)

Author: vladitasev

packages/base/src/sap/ui/webcomponents/base/Bootstrap.js

@@ -2,6 +2,7 @@ import whenDOMReady from "./util/whenDOMReady";
 import EventEnrichment from "./events/EventEnrichment";
 import { insertIconFontFace } from "./IconFonts";
 import DOMEventHandler from "./DOMEventHandler";
+import whenPolyfillLoaded from "./compatibility/whenPolyfillLoaded";
 
 EventEnrichment.run();
 
@@ -14,22 +15,12 @@ const Bootstrap = {
 			return bootPromise;
 		}
 
-		bootPromise = new Promise(resolve => {
-			whenDOMReady().then(() => {
-				insertIconFontFace();
-				DOMEventHandler.start();
-
-				if (window.WebComponents && window.WebComponents.waitFor) {
-					// the polyfill loader is present
-					window.WebComponents.waitFor(() => {
-						// the polyfills are loaded, safe to execute code depending on their APIs
-						resolve();
-					});
-				} else {
-					// polyfill loader missing, modern browsers only
-					resolve();
-				}
-			});
+		bootPromise = new Promise(async resolve => {
+			await whenDOMReady();
+			insertIconFontFace();
+			DOMEventHandler.start();
+			await whenPolyfillLoaded();
+			resolve();
 		});
 
 		return bootPromise;

packages/base/src/sap/ui/webcomponents/base/compatibility/whenPolyfillLoaded.js

@@ -0,0 +1,24 @@
+let polyfillLoadedPromise;
+
+const whenPolyfillLoaded = () => {
+	if (polyfillLoadedPromise) {
+		return polyfillLoadedPromise;
+	}
+
+	polyfillLoadedPromise = new Promise(resolve => {
+		if (window.WebComponents && window.WebComponents.waitFor) {
+			// the polyfill loader is present
+			window.WebComponents.waitFor(() => {
+				// the polyfills are loaded, safe to execute code depending on their APIs
+				resolve();
+			});
+		} else {
+			// polyfill loader missing, modern browsers only
+			resolve();
+		}
+	});
+
+	return polyfillLoadedPromise;
+};
+
+export default whenPolyfillLoaded;