The read-only charLength property of the SpeechSynthesisEvent interface returns the number of characters left to be spoken after the character at the charIndex position.
If the speech engine can't determine it, it returns 0.
An integer.
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.",
);
}
};