Callback in chrome.tts.speak?

Question

I am trying to call a callback function after chrome.tts.speak has finished the speech, and there is a nice argument space for that. But, after looking for more detail about it, very disappointingly, this is what the document says:

callback ( optional function )
　　Called right away, before speech finishes.

And I don't want it to be called right away. I want it after the speech is finished. So is it possible? Any method is welcomed. (but not so "hacky")

Answer 1

In the same page, it mentions onEvent (as part of options):

onEvent ( optional function )
　　This function is called with events that occur in the process of speaking the utterance.
　　Parameters
　　event ( TtsEvent )
　　　　The update event from the text-to-speech engine indicating the status of this utterance.

TtsEvent has a type property, which can be end to mark the speech ending. Put it together:

chrome.tts.speak("Hello, world!", {
    requiredEventTypes: ['end'],
    onEvent: function(event) {
        if(event.type === 'end') {
            alert('Speech ended.');
        }
    }
});