In the end the target is web assembly, so even writing the code directly in js would require some compilation. Why C and not an other language that can be compiled to web assembly? I guess that was mostly a question of taste.

Ah, the web assembly target is for performance? I'm curious about the process of getting from 'let's put Stellarium on the web' to 'we're going to do a clean, pruned rewrite in C and spit out web assembly'. Like, did you sit around and think deep thoughts about various options? Or did someone look at web assembly and think 'huh, webassembly might be a neat way to port Stellarium to the web'.

I think it was mostly because we knew we could do it this way. Having a C code base is also nicer for integrating back into Stellarium desktop, do other platform ports, etc.

Makes sense, thanks for indulging my nosiness!