Add web front-end and fix API issues

node_modules/rxjs/dist/esm/internal/operators/throwIfEmpty.js

@@ -0,0 +1,16 @@
+import { EmptyError } from '../util/EmptyError';
+import { operate } from '../util/lift';
+import { createOperatorSubscriber } from './OperatorSubscriber';
+export function throwIfEmpty(errorFactory = defaultErrorFactory) {
+    return operate((source, subscriber) => {
+        let hasValue = false;
+        source.subscribe(createOperatorSubscriber(subscriber, (value) => {
+            hasValue = true;
+            subscriber.next(value);
+        }, () => (hasValue ? subscriber.complete() : subscriber.error(errorFactory()))));
+    });
+}
+function defaultErrorFactory() {
+    return new EmptyError();
+}
+//# sourceMappingURL=throwIfEmpty.js.map