This is a simple demo showing how to get WebGL2 working via the Wasm/Emscripten target of Rust. Code is fully adopted from the gl-rs triangle example.
You'll need Rust-1.22 or newer as well as Emscripten SDK installed.
In Emscripten configuration, set USE_WEBGL2=1. I did it by just modifying emscripten/src/settings.js directly (from where it's installed). Hopefully, we'll be able to pass the linker parameters to emcc via cargo one day.
rustup target add wasm32-unknown-emscripten
cargo build --target=wasm32-unknown-emscripten
firefox triangle.html