Screenreader + TTS not working correctly

Hey everyone!
I have this function here:

import { Component } from '@angular/core';
import { NavController } from 'ionic-angular';
import { MobileAccessibility } from '@ionic-native/mobile-accessibility';
import { TextToSpeech } from "@ionic-native/text-to-speech";

  selector: 'page-home',
  templateUrl: 'home.html',

export class HomePage {

  constructor(public navCtrl: NavController, private mobileAccessibility: MobileAccessibility, private tts: TextToSpeech) {

    // TalkBack for Android
    document.addEventListener('deviceready', function () {
        .then(value => {
          if (value) {
            alert("Screen reader: ON");
              text: 'Page has loaded successfully.',
              locale: 'en-US',
              rate: 0.75
          } else {
            return false;
          return true;

Important: TTS should ONLY work if the devices screen reader is activated! The TTS should say “Page loaded successfully” and then completely turn off. After that, the vision impaired person shpuld be able to navigate through the page by using the devices activated screen reader.

Problem: Both, TTS and screen reader, are talking. First, the TTS speaks (i.e. “Button Home, Home Page”) and then the screen reader repeats the same and so on… The only thing that works is that TTS only works when the screen reader is activated.

What did I miss that my code isn’t working correctly? I used the promise part of the plugin’s definition… but I honestly don’t know how I could make the promise part function …