How to handle back button event such as on android

Questions
1

Q: if a panel ( or dialog, notification and so on). is open, I want only close it not navigate previous page.

My code below:

import { f7 } from 'framework7-react';

const handlerBackPress: (): void => {
    const canGoBack = f7.views.main.router.history.length > 1;
    if (canGoBack) {
       f7.views.main.router.back();
    } else {
      // handlerExitApp;
    }
}

const startApp = (): void => {
  ReactDOM.render(React.createElement(App), document.getElementById('root'));
  document.addEventListener('backbutton', handlerBackPress, false);
};

document.addEventListener('deviceready', startApp, false);

"framework7": "5.0.4",
"framework7-react": "5.0.4",
"cordova-android": "8.1.0",
"cordova-ios": "5.0.1",
2

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