What do WebASM, Reason, Dart, Rust, and Go all have in common? They're all trying to make the web faster. However, they do it in different ways.
WebASM's approach is obvious. Take high performance code written in C and C++. Find a way to run it safely in the browser.
Go is a language aimed at replacing server-side C++. However, they're working on compiling to WebASM as well.
Rust is a language aimed at replacing C++ as well, but it was originally written specifically for reimplementing Firefox in order to make the browser faster. It too can be compiled to WebASM.