Wait for "onvoiceschanged" in Chrome

[stefan-niedermann]

According to the MDN docs one needs to wait in Chrome browsers for the onvoiceschanged event. This does not work on Firefox, therefore Mozilla suggests this approach:

var voices = [];

function populateVoiceList() {
  voices = synth.getVoices();
  // Now we have the voices.
}

populateVoiceList();
if (speechSynthesis.onvoiceschanged !== undefined) {
  speechSynthesis.onvoiceschanged = populateVoiceList;
}

It would be nice if the SpeechSynthesisService.getVoices() would return a Promise or an Observable.

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