You want that your users can leave messages in your Angular Application. In this Article I explain how you can implement this with Angular 4 and Firebase. First we have to import the Moduls for Firebase in our app.module.ts and our component. app.module.ts import { AngularFireModule } from 'angularfire2' ; import { AngularFireDatabaseModule , AngularFireDatabase , FirebaseListObservable } from 'angularfire2/database' ; @ NgModule ({ declarations: [ AppComponent ], imports: [ BrowserModule , FormsModule , HttpModule , AngularFireModule . initializeApp ( firebaseConfig ), AngularFireDatabaseModule , We also have to configure the AngularFireModule. export const fireba...