Although WebAssembly brings languages other than HTML, CSS and JavaScript to the browser, it’s not a JavaScript replacement and it takes a very different approach from Flash, Active X plugins and other techniques that encapsulated non-web code for browsers. Think of it as a small, fast, efficient and very secure, stack-based virtual machine that doesn’t care what CPU or OS it runs on, that’s designed to execute portable bytecode — compiled from code originally written in C, C++, Rust, Python or Ruby — at near-native speed. WebAssembly doesn’t only run in the browser: It started on the client, but is proving very useful on the server.
Source: The New Stack