https://medium.com/@robaboukhalil/porting-games-to-the-web-with-webassembly-70d598e1a3ec

WebAssembly is a new language for the web. Much like low-level assembly languages, however, very few people write WebAssembly by hand; instead, you can compile code written in other languages (e.g. C, C++ and Rust) to WebAssembly and run that code in the browser.

Why would you ever want to do that, you ask? One reason is portability: WebAssembly makes it easier to port existing games, desktop applications, and command-line tools to the web. Another reason is the potential for speeding up web apps by replacing slow JavaScript calculations with compiled WebAssembly.