Android hardware back button in ionic

[NyaO]

Here is solution for Ionic 2:

constructor(
    public platform: Platform, //Platform controller
    public app: App, //App controller
  ) {
    platform.ready().then(() => {
      StatusBar.styleDefault();
      Splashscreen.hide();

      //Registration of push in Android and Windows Phone
      platform.registerBackButtonAction(() => {
        let nav = this.app.getActiveNav();
        if (nav.canGoBack()){ //Can we go back?
          nav.pop();
        }else{
          this.platform.exitApp(); //Exit from app
        }
      });
    });
  }