Supporting native Rust in Workers with the new Emscripten target for wasm-bindgen

What happened

With the new experimental support for the Emscripten target in Rust Workers, many previously unsupported Rust libraries and applications can now be built and deployed directly to Cloudflare’s global Workers platform, including upcoming support for Tokio async. Enabling the Emscripten target for wasm-bindgen has been a long-term effort, first initiated by Google over a year ago, and then further reviewed and supported by the Cloudflare engineers maintaining wasm-bindgen.

The goal was for wasm-bindgen to drive the build and produce the companion JavaScript, while Emscripten’s linker (wasm-ld) would be able to link in any C++ dependencies needed. Internally, Google operates with Emscripten in C++ codebases to generate JavaScript along with the rest of their applications, allowing the C++ and JS to interact with one another. While Emscripten was capable of linking in Rust code as a dependency, the thing it couldn’t do was provide a robust binding system between Rust and JavaScript like wasm-bindgen does.

Key facts

• Internally, Google — uses: Emscripten in C++ codebases to generate JavaScript along with the rest of their applications, allowing the C++ and JS to interact with one another