Uncaught TypeError: Cannot read property 'call' of undefined

Per #624, I'm trying to figure out a way to inject captions into TimeLineJS3 for my local videos without modifying the source code itself. Unfortunately, I'm running into difficulties when using the events as specified here:

https://github.com/NUKnightLab/TimelineJS3/blob/master/API.md

I can get the event "loaded" to work, but when I try "nav_next" or "change," I get the following error:

timeline.js:2514 Uncaught TypeError: Cannot read property 'call' of undefined at NewClass.fireEvent (timeline.js:2514) at NewClass._onStorySliderNext (timeline.js:14008) at NewClass.fireEvent (timeline.js:2514) at NewClass._onNavigation (timeline.js:10903) at NewClass.fireEvent (timeline.js:2514) at NewClass._onMouseClick (timeline.js:10366) at HTMLDivElement.handler [as _tl_click7] (timeline.js:5296) fireEvent @ timeline.js:2514 _onStorySliderNext @ timeline.js:14008 fireEvent @ timeline.js:2514 _onNavigation @ timeline.js:10903 fireEvent @ timeline.js:2514 _onMouseClick @ timeline.js:10366 handler @ timeline.js:5296

Now, I may not be using the event correctly, so here's my JS code:

`
// these are the major functions that inject events/code into TL (for benevolent reasons, of course)
function tlHijack () {
console.log(timeline.getDataById(timeline.current_id));
}

function init () {

    // add an event to handle the arrow keys so that they pause the videos
    document.addEventListener ("keyup", handleKeys, true);

    // when the user swipes between events, also pause the videos
    document.getElementById("timeline-embed").addEventListener("touchmove", pauseVideos, false);

    // finally, if the user clicks on either arrow, pause the videos

    //timeline.on("change", console.log("next..."));
    timeline.on("nav_next", tlHijack());

}

window.onload = init;
`

And here's the HTML:

`

<title>audio formats timeline</title>

<link title="timeline-styles" rel="stylesheet" href="https://cdn.knightlab.com/libs/timeline3/latest/css/timeline.css">
<link title="timeline-styles" rel="stylesheet" href="https://cdn.knightlab.com/libs/timeline3/latest/css/fonts/font.default.css">

<script src="https://cdn.knightlab.com/libs/timeline3/latest/js/timeline.js"></script>
<script src="https://mosterd.org/common/js/timelineListeners.js"></script>

<script> timeline = new TL.Timeline('timeline-embed', '{my spreadsheet URL}'); </script> ` Where "{my spreadsheet URL}" is the link to my Google spreadsheet.

Any idea what might be going on?

Start with API.md's event examples and the event registration in timelineListeners.js, then reproduce the nav_next and change interactions from the issue. Trace the calls through timeline.js fireEvent, _onStorySliderNext, and _onNavigation; done means the documented events can be registered and triggered without the reported TypeError.