yo-wasm-integration

name	yo-wasm-integration
description	Build Yo libraries for WebAssembly and publish as npm packages. Use this when working with WASM targets, Emscripten, WASI, npm packaging, JavaScript/TypeScript wrappers, or browser/Node.js integration.
argument-hint	[WASM task, target, or integration question]

Yo WASM Integration

Use this skill for compiling Yo projects to WebAssembly and packaging them for JavaScript/TypeScript consumption via npm.

When to use this skill

Use this skill when you need to:

• compile a Yo project to WebAssembly (Emscripten or WASI)
• set up an npm/ package directory with JavaScript/TypeScript wrappers
• expose Yo functions to JavaScript via WASM memory and C ABI
• integrate a Yo WASM module into a Node.js or browser project
• debug WASM-specific compilation or runtime issues
• publish a Yo-backed npm package

Workflow

1. Decide on target: Emscripten (browser + Node.js) or WASI (standalone/server).
2. Define WASM build steps in build.yo using build.executable with target: build.CompilationTarget.Wasm32_Emscripten and add_c_flags(...) for Emscripten settings.
3. Create a JavaScript wrapper in npm/ that loads the WASM module and exposes a clean API.
4. Add TypeScript declarations (index.d.ts) for type safety.
5. Test the WASM module from both Node.js and browser contexts.
6. Consult the WASM integration cheatsheet for patterns.

High-signal rules

• In build.yo, use target: build.CompilationTarget.Wasm32_Emscripten for Emscripten WASM builds. Use step.add_c_flags(...) for Emscripten -s options.
• For single-file compilation, use yo compile --cc emcc or yo compile --target wasm-wasi.
• WASM functions communicate through linear memory — pass pointers and lengths, not Yo types.
• JavaScript wrappers handle the string encoding/decoding boundary (TextEncoder/TextDecoder).
• Use bitmask flags (powers of 2) to pass option sets through a single i32 parameter.
• Yo's str and String types are internal — export raw *(u8) + usize pairs for WASM APIs.
• Always test with --sanitize address on native first, then verify WASM behavior matches.
• Emscripten exports are controlled by -sEXPORTED_FUNCTIONS and -sEXPORTED_RUNTIME_METHODS.
• WASM modules can be loaded in Node.js using WebAssembly.instantiate or Emscripten's generated JS glue.
• Errno values differ on WASM — use constants from std/libc/errno, never hardcode numbers.

Resource

• WASM integration cheatsheet