Add web front-end and fix API issues

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

@@ -0,0 +1,13 @@
+import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError';
+import { filter } from './filter';
+import { throwIfEmpty } from './throwIfEmpty';
+import { defaultIfEmpty } from './defaultIfEmpty';
+import { take } from './take';
+export function elementAt(index, defaultValue) {
+    if (index < 0) {
+        throw new ArgumentOutOfRangeError();
+    }
+    const hasDefaultValue = arguments.length >= 2;
+    return (source) => source.pipe(filter((v, i) => i === index), take(1), hasDefaultValue ? defaultIfEmpty(defaultValue) : throwIfEmpty(() => new ArgumentOutOfRangeError()));
+}
+//# sourceMappingURL=elementAt.js.map