Updating & Patching game files

i have a problem, im making a game launcher and i want to add an update function. The idea is that this update function checks differences in files and download only the changed ones or new ones as the game weight is more than 1Gb and its not funny to redownload it all.

The thing is that i dont know how to make it. The Launcher was made with electron so i understand it should be ideal to done this in javascript.

Please any help would be great.

I saw a similar post that recommends using bsdiff & bspatch but that only works in .NET.