Add web front-end and fix API issues

node_modules/rxjs/dist/esm5/internal/operators/elementAt.js

@@ -0,0 +1,15 @@
+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();
+    }
+    var hasDefaultValue = arguments.length >= 2;
+    return function (source) {
+        return source.pipe(filter(function (v, i) { return i === index; }), take(1), hasDefaultValue ? defaultIfEmpty(defaultValue) : throwIfEmpty(function () { return new ArgumentOutOfRangeError(); }));
+    };
+}
+//# sourceMappingURL=elementAt.js.map