Io

What is Io? Example Code Quick Links Platform Building Running Browser REPL Running Tests Extending Io Io targets WebAssembly. A single WASI binary runs under any WASI host (wasmtime, Node, browsers via WASI shims) and ships with a browser REPL and a bidirectional Io↔JavaScript bridge. If you need the previous native build (CMake, dynamic addons, Eerie package manager), use the native branch or the 2026.04.20-native-final tag. The native path accepts bug fixes; new development lands on master . make Build build/bin/io static (WASI CLI binary) make test Build build/bin/test iterative eval make check Run both test suites under wasmtime make browser Build browser/io browser.wasm (browser REPL) make serve Serve the browser REPL at make check-browser Run browser tests under Playwright make regenerate Regenerate IoVMInit.c from .io sources make clean Remove build artifacts Run a script (pass --dir=. so the WASI sandbox can read the file): Then open . See browser/README.md for details on embedding the REPL in a page and calling between Io and JavaScript. The native addon system ( DynLib , AddonLoader , Eerie) is not available on WebAssembly. Host integration goes through the JavaScript bridge instead: Io code can call JS functions, and JS can call Io methods. See browser/README.md and agents/wasm/Bridge.md .