Computers have take million of man hours to get to the point where we are today, you are standing on the shoulders of giants, building things from scratch is nearly impossible.
you don’t want to use any other programs, but you do want to use unity? That is contradicting.
i don’t know where you get your information, but that is just inaccurate.
you can make games (desktop version) with things like appJS, but personally, i would pick a better language for the job. And use an existing game engine (like unity with c#, unreal engine 4 (which uses c++ i believe) or any other engine), you can google for more game engines.