When I was finished with Serenum API, I started over with the website Serenum to show the data from the API with style.
I built the website with no JavaScript first, building for an example the bar charts with HTML and CSS by hand. After everything was done, I added 2 features with JavaScript: getting your current location 1 time with GPS and adding a map from Leaflet for choosing a place with it.
Thanks to this strategy, Serenum works perfectly with and without JavaScript.
The website are far from done, though. Both astronomical calculations and light theme are missing, more features with JavaScript will be added, and more.