How return a handler button result in ionic 4 as promise

I had this ionViewCanLeave method to can leave a page. Now, in ionic 4, I have to use a guard with canDeactivate. But I need to convert this code to return a promise but only when a button (ok or cancel) is clicked.

  canDeactivate(): boolean | Promise<boolean> | Observable<boolean> {
    // If the support message is empty we should just navigate
    if (!this.f.controls['consulta'].value || this.f.controls['consulta'].value.trim().length === 0) {
      return true;
    // return this.confirmDialogService.confirm('Quieres cancelar el mensaje? Tu mensaje no será enviado!');
    return new Promise((resolve: any, reject: any) => {
        header: 'Abandonar?',
        message: 'Quieres cancelar el mensaje? Tu mensaje no será enviado!',
        buttons: [
          { text: 'Permanecer', handler: reject },
          { text: 'Abandonar', role: 'cancel', handler: resolve }
      }).then(alert => alert.present());


I have tried some options, but nothing works. But I use a window.confirm instead an alertCtrl, works as expected, like this:

    confirm(message?: string): Observable<boolean> {
        const confirmation = window.confirm(message || 'Are you sure?');
        return Observable.of(confirmation);

Someone can help me?

{ text: 'Permanecer', handler: reject(false) },
{ text: 'Abandonar', role: 'cancel', handler: resolve(true) }