Is libsoduim written in a low level language like c or did they compile javascript down to webassembly somehow? It wasn't clear from the article. At least my reading of it.
libsodium is written in c. "Pure javascript" is a supported compilation target[0] of the project. Emscripten is used to compile the c to javascript. There's also now a wasm compilation target, again via emscripten.
The c source code is really excellent[1]. It's worth browsing!
[0]-https://github.com/jedisct1/libsodium.js [1]-https://github.com/jedisct1/libsodium/tree/master/src/libsod...