Added persistent login

src/app/login/login.guard.ts

@@ -1,17 +1,23 @@
 import {CanActivate, Router} from '@angular/router';
 import {firebaseApp} from '../app.module';
 import {Injectable} from '@angular/core';
+import {Observable, timer} from 'rxjs';
+import {filter, map} from 'rxjs/operators';
 
 @Injectable({
     providedIn: 'root'
 })
 export class LoginGuard implements CanActivate {
+    loggedIn?;
 
-    constructor(private router: Router) {}
+    constructor(private router: Router) {
+        firebaseApp.auth().onAuthStateChanged(user => this.loggedIn = !!user);
+    }
 
-    canActivate() {
-        let valid = !!firebaseApp.auth().currentUser;
-        if(!valid) this.router.navigate(['/login']);
-        return valid;
+    canActivate(): Observable<boolean> {
+        return timer(0, 100).pipe(filter(() => this.loggedIn != null), map(() => {
+            if(!this.loggedIn) this.router.navigate(['/login']);
+            return this.loggedIn;
+        }));
     }
 }