arcsecond | ✨Zero Dependency Parser Combinator Library for JS | Parser library

I am making a unit converter app. It works well except for one issue. When I change the value of the second and third pickers and then change the value of the first picker, the app crashes. I suspect that this is because it is being set to an index out of range. Is there any way to fix this? Is it possible to set the values of fromUnitsIndex and toUnitsIndex back to 0 when the value of unitTypesIndex changes?

Here is the code:

I'm making figures of some galaxies velocities with matplotlib, from some .fits files. The problem is that the axes in the figure show the galaxy's size in pixels, and I want to display them as Declination and RightAcension (in angle units). I already know that each pixel has a size of 0.396 arcseconds. How can I convert pixels to arcseconds in both X and Y axes?

The code is the folowing:

I'm working on an astronomical database program that allows users to create and enter their own stars and brown dwarfs, among other things, for an entry-level programming course at university. Each object has xyz coordinates that determine its position in space, with the Sun being at 0, 0, 0 light years.

However, since a lot of star databases (e.g. SIMBAD), Wikipedia, etc., give astronomical objects' positions in terms of parallax angles and right ascension/declination coordinates, I've given users the option to add objects using those parameters, in case they don't have xyz coordinates. I'm having problems with getting it to provide accurate values though.

Here's the code for entering parallax angle, with options for entering in both arcseconds/as and milliarcseconds/mas: