Compiling C/C++ to WebAssembly with Emscripten: High-Performance Browser Modules

When browser applications need near-native CPU performance for audio DSP, video transcoding, cryptography, or neural network inference, compiling C/C++ libraries to WebAssembly (WASM) with Emscripten (`emcc`) unlocks deterministic SIMD execution directly inside Web Workers.

1. Exporting C Functions to JavaScript with `EMSCRIPTEN_KEEPALIVE`

#include <emscripten/emscripten.h>

extern "C" {
  EMSCRIPTEN_KEEPALIVE
  float dot_product(const float* a, const float* b, int length) {
    float sum = 0.0f;
    for (int i = 0; i < length; ++i) {
      sum += a[i] * b[i];
    }
    return sum;
  }
}

2. Compiling Modular ES6 WASM Bundles

emcc math_kernel.cpp -O3 -msimd128 \
  -s WASM=1 \
  -s MODULARIZE=1 \
  -s EXPORT_ES6=1 \
  -s EXPORTED_RUNTIME_METHODS='["ccall","cwrap","HEAPF32"]' \
  -o math_kernel.js