An Ionic Cordova AngularJS back button working on the TABS example

app.compentent.ts

import { Component, ViewChild } from '@angular/core';
import { App, Platform, AlertController } from 'ionic-angular';
import { SplashScreen } from '@ionic-native/splash-screen';
import { StatusBar } from '@ionic-native/status-bar'; 
import { TabsPage } from '../pages/tabs/tabs';
import { WelcomePage } from '../pages/welcome/welcome'; 
import { IonicPage, NavController, NavParams } from 'ionic-angular';

 @Component({
  template: `<ion-nav [root]="rootPage"></ion-nav>`
})
export class MyApp {
  rootPage = TabsPage;
  
  @ViewChild('root') navCtrl: NavController;
  
    constructor(public platform: Platform,
                statusBar: StatusBar,
                splashScreen: SplashScreen,
                public  app: App,
                public alertCtrl: AlertController 
                )
    {
        platform.ready().then(() => {
            statusBar.styleDefault();
            splashScreen.hide(); 
            
            // https://www.gajotres.net/ionic-2-3-how-to-manage-hardware-back-button-event-like-a-pro/2/
            let nav = app.getActiveNavs()[0]; 
            platform.registerBackButtonAction(() =>
            {
 
                let nav = app.getActiveNavs()[0];
                let activeView = nav.getActive();                
  
                if((activeView.name === "WelcomePage") || (activeView.name === "AboutPage") || (activeView.name === "HomePage") || (activeView.name === "ContactPage"))
                { 
                    if (nav.canGoBack()){ //Can we go back?
                        nav.pop();
                    } else {
                        const alert = this.alertCtrl.create({
                            title: 'App termination',
                            message: 'Do you want to close the app?',
                            buttons: [{
                                text: 'Cancel',
                                role: 'cancel',
                                handler: () => {
                                    console.log('Application exit prevented!');
                                }
                            },{
                                text: 'Close App',
                                handler: () => {
                                    this.platform.exitApp(); // Close this application
                                }
                            }]
                        });
                        alert.present();
                    }
                } else
                { 
                 if (nav.canGoBack())
                  { //Can we go back?
                   nav.pop();
                  } 
                }
            }); 
            
        });
    }
}

This example was originally taken from here
https://www.gajotres.net/ionic-2-3-how-to-manage-hardware-back-button-event-like-a-pro/2/
https://github.com/Gajotres/IonicBackButtonHandleExample/blob/master/src/app/app.component.ts

But I needed a little something extra, as the back button just didn't work as expected.
If you navigated to all the different tabs, the back button would only work on the "HomePage". It felt like the app just wasn't working.
So, this at least gives you the option to quit if you are on any of the defined tab pages that you set.

I also added this to the original author's 'bug' tracker. Not as a bug, but a suggestion/thankyou.
Gajotres/IonicBackButtonHandleExample#2