You're code looks great, I'm struggling to find areas to push you, that said, I doubt this is going to change, it should probably be const. There are a few more variables that I see should probably be consts also.

This is pretty awesome, but it's not finished. Your readme is weak. Well nonexistent really. I asked for a mildly detailed readme. Described what you did with the API, provide some code samples, give some opinion, use a little formatting, provide an install usage guide.

... and it should probably be const.

.. after it's instantiated might as well call this.reset() in the constructor?

You're building objects with methods and defining a init method even. Might as well turn this into a class. This is sort of the same thing but with built in convention. It will also enforce good coding habits.

... these js function calls in HTML attributes. To be honest I'm not really sure whether this is best practice or not, I suspect not. I suppose you might say it couples your implementation to your HTML structure. It's probably more flexible in the long term to use an id and add a listener. Which you are doing in other places, which makes this look inconsistent.

I'll leave it up to you, but I recommend against this.

Overall your code looks pretty advanced. Looks like you have a lot of experience with JS. It also look like you are coding without a lot of the new features. You should stretch yourself by trying to incorporate as many of the newer features s you can.

You probably wrote this for loop on automatic. But this var could be a let. I think this is best practice these days, and will be in the future.