I know procedural programming languages reasonably well, but have next to zero JS skills. So my contribution could be usage, suggestions and maybe the occasional trivial fix.
That does not deter me from wishful thinking ;) - what trajectory viewers IMO are missing is the ascent and descent phase. So in my case that'd be:
forward and backward trajectories for a given location and altitude
refine with a ascent/descent rate for the takeoff and landing phase