Confirmation dialog before quitting the app Ionic6

Question

I wonna show confirmation dialog before user will quit app.

I found this instruction in the docs

import { useBackButton, useIonRouter } from '@ionic/vue';
import { Plugins } from '@capacitor/core';
const { App } = Plugins;

...

export default {
  setup() {
    const ionRouter = useIonRouter();
    useBackButton(-1, () => {
      if (!ionRouter.canGoBack()) {
        App.exitApp();
      }
    });
  }
}

How I can call custom function from methods section?

...
if (!ionRouter.canGoBack()) {
     this.doExitApp();
}
...

Android Studio show error

Msg: TypeError: Cannot read property 'doExitApp' of undefined

Link on the doc

https://ionic-docs.herokuapp.com/docs/fr/developing/hardware-back-button