first working state

services/alert.service.js

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+import { Subject } from "rxjs";
+import { filter } from "rxjs/operators";
+
+export const alertService = {
+  onAlert,
+  success,
+  error,
+  info,
+  warn,
+  alert,
+  clear,
+};
+
+export const AlertType = {
+  Success: "Success",
+  Error: "Error",
+  Info: "Info",
+  Warning: "Warning",
+};
+
+const alertSubject = new Subject();
+const defaultId = "default-alert";
+
+// enable subscribing to alerts observable
+function onAlert(id = defaultId) {
+  return alertSubject.asObservable().pipe(filter((x) => x && x.id === id));
+}
+
+// convenience methods
+function success(message, options) {
+  alert({ ...options, type: AlertType.Success, message });
+}
+
+function error(message, options) {
+  alert({ ...options, type: AlertType.Error, message });
+}
+
+function info(message, options) {
+  alert({ ...options, type: AlertType.Info, message });
+}
+
+function warn(message, options) {
+  alert({ ...options, type: AlertType.Warning, message });
+}
+
+// core alert method
+function alert(alert) {
+  alert.id = alert.id || defaultId;
+  alert.autoClose = alert.autoClose === undefined ? true : alert.autoClose;
+  alertSubject.next(alert);
+}
+
+// clear alerts
+function clear(id = defaultId) {
+  alertSubject.next({ id });
+}

services/index.js

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+export * from "./alert.service";