Wasm Emscripten

WebAssembly with Emscripten

Purpose

Guide agents through compiling C/C++ to WebAssembly using Emscripten: emcc flag selection, function exports, memory model configuration, Asyncify for asynchronous C code, debugging WASM binaries, and targeting WASI vs browser.

Triggers

• "How do I compile C to WebAssembly with Emscripten?"
• "How do I export a C function to JavaScript?"
• "How does WebAssembly memory work with Emscripten?"
• "How do I debug a .wasm file?"
• "How do I use Asyncify to make synchronous C code async?"
• "What's the difference between WASI and Emscripten browser target?"

Workflow

1. Setup and first build

# Install Emscripten SDK
git clone https://github.com/emscripten-core/emsdk.git
cd emsdk
./emsdk install latest
./emsdk activate latest
source ./emsdk_env.sh    # add emcc to PATH

# Verify
emcc --version

# Compile C to WASM (browser target)
emcc hello.c -o hello.html          # generates hello.html + hello.js + hello.wasm
emcc hello.c -o hello.js            # just JS + WASM (no HTML shell)

# Serve locally (WASM requires HTTP, not file://)
python3 -m http.server 8080
# Open: http://localhost:8080/hello.html