If I understand correctly, what this project does is take the actual postgresql sources, which are written in C, compile them to wasm and provide typescript wrappers. So you need the wasm to be able to use the C code from js/ts.
Looking at the repo, it started as postgres-in-the-browser. An abstract interface with C and wasm as targets is just more scope.
But it looks like the hard part of patching postgres to librar-ify it is already done agnostically in C.
So you just need to ctrl-f for "#if defined(__EMSCRIPTEN__)" to impl those else branches and port the emmake file to make.