The charIndex read-only property of the SpeechSynthesisUtterance interface returns the index position of the character in the SpeechSynthesisUtterance.text that was being spoken when the event was triggered.
The elapsedTime read-only property of the SpeechSynthesisUtterance interface returns the elapsed time in milliseconds after the SpeechSynthesisUtterance.text started being spoken that the event was triggered at.
The name read-only property of the SpeechSynthesisUtterance interface returns the name associated with certain types of events occuring as the SpeechSynthesisUtterance.text is being spoken: the name of the SSML marker reached in the case of a mark event, or the type of boundary reached in the case of a boundary event.
The utterance read-only property of the SpeechSynthesisUtterance interface returns the SpeechSynthesisUtterance instance that the event was triggered on.