Check firebase logged in state

loader.html

<ion-content>
  <ion-spinner ion-fixed></ion-spinner>
</ion-content>

loader.scss

page-loader {
    .fixed-content {
        display: flex;
        align-items: center;
        justify-content: center;
    }
}

loader.ts

import { Component } from '@angular/core';
import { NavController, NavParams } from 'ionic-angular';

import { AngularFireAuth, FirebaseAuthState } from 'angularfire2';

import { WelcomePage } from '../welcome/welcome';
import { SplitPage } from '../split/split';

@Component({
  selector: 'page-loader',
  templateUrl: 'loader.html'
})
export class LoaderPage {

  constructor(
    public navCtrl: NavController,
    public navParams: NavParams,
    public auth$: AngularFireAuth
  ) {
    let authSubscription = auth$.subscribe((state: FirebaseAuthState) => {
      // Stop checking for auth status change
      authSubscription.unsubscribe();
      // state.uid
      if (state === null) {
        navCtrl.setRoot(WelcomePage);
      } else {
        this.navCtrl.setRoot(SplitPage);
      }
    });
  }

}