How to Exit on root pages from app - Ionic4

Ionic Framework ionic-v3
1

HI All,
This question is regarding how to close the application once the user clicks on the **Hardware Back Button** of the device from the root pages of the application. Currently I am using the following method for back button action.

this.platform.backButton.subscribe(async () => {

}

I am facing the issue when the user reaches the root page and pres the back-button again. The application should close. But it didnt. The code that I am using is

this.routerOutlets.forEach((outlet: IonRouterOutlet) => {
                if (outlet && outlet.canGoBack()) {
                    outlet.pop();

                } else if (this.router.url === '/home') {
                    if (new Date().getTime() - this.lastTimeBackPress < this.timePeriodToExit) {
                        // this.platform.exitApp(); // Exit from app
                        navigator['app'].exitApp(); // work in ionic 4

                    } else {
                        this.toast.show(
                            `Press back again to exit App.`,
                            '2000',
                            'center')
                            .subscribe(toast => {
                                // console.log(JSON.stringify(toast));
                            });
                        this.lastTimeBackPress = new Date().getTime();
                    }
                }
            });

is there any mistake in my code?

Thanks and Regards
Anand Raj