SpeechSynthesisEvent: свойство charLength

utterThis.onpause = (event) => {
  const char = event.utterance.text.charAt(event.charIndex);
  const charLeft = event.charLength;
  if (charLeft) {
    console.log(
      `Speech paused. There are still ${charLeft} characters to be spoken.`,
    );
  } else {
    console.log(
      "Speech paused. The underlying speech engine can't tell how many characters are left.",
    );
  }
};