Litepicker | Date range picker - lightweight , no dependencies | Date Time Utils library

I am working on building a date picker using the litepicker.js I have everything working so far but got stumped on getting the endDate to load tomorrows date. Here is what I currently have.

I'm trying to use Litepicker on a webpage through Typescript, but the emitted JS can't load the module. This is what I have:

index.html

Background:

I used the Litepicker library in my project and spotted a bug where displayed month names are off by one. E.g. "February" is labelled "January". The dates are exported correctly. It is not a problem with months starting from zero. Only translations are "off by one".

When I tried to reproduce the issue, it looks like Litepicker works correctly. The documentation says it uses Date.prototype.toLocaleString() internally, so I believe one of our dependencies modifies it.

Question:

How can I check which dependency/piece of code modifies Date.prototype? Is there a reflection mechanism that could tell me who tinkered with it?

Im currently working on a little project and I have been asked to do some specific styling to a date picker - this date picker library is using LitePicker.js. The only issue is to do it i'd need an extra div inside the current anchor which contains the date.

Currently the html looks like this:

11

but I need it to look like this:

11

In the documentation there is no example on how I could do this via the api:

https://wakirin.github.io/Litepicker/

Would I be able to use the THIS method within the same scope to append a span tag to do this?

Here is the basics of the setup in CodePen:

https://codepen.io/nolimit966/pen/ZEQEawv

Any help would be really appreciated.

Thank you