btn.dispatchEvent(
document.createEvent("MouseEvent")
.initMouseEvent("click", true, true, window, 0,
0, 0, 0, 0,
false, false, false, false,
0, null)
);
Your problem is that initMouseEvent
doesn't return anything. You can't combine all of that into one line. You need to break it up.
var mEvent = document.createEvent("MouseEvent");
mEvent.initMouseEvent("click", true, true, window, 0,
0, 0, 0, 0,
false, false, false, false,
0, null);
btn.dispatchEvent(mEvent);
This is how it's done in the demo you linked to.