emscripten_keydown_sample.cxx

#include <iostream>
#include <queue>
#include <emscripten/emscripten.h>
#include <emscripten/bind.h>

namespace
{
  std::queue<unsigned int> keydown_buffer;

  auto cxx_keydown(unsigned int key_code)
    -> void
  {
    EM_ASM({ console.log("cxx_keydown") });
    keydown_buffer.push(key_code);
  }
  
  EMSCRIPTEN_BINDINGS(my_module)
  { emscripten::function("cxx_keydown", &cxx_keydown); }
  
}

auto main() -> int
{
  EM_ASM({ window.addEventListener("keydown", function(e){ Module.cxx_keydown(e.keyCode); }); });
  
  emscripten_set_main_loop
  ( []
    {
      while(!keydown_buffer.empty())
      {
        std::cerr << keydown_buffer.front() << "\n";
        keydown_buffer.pop();
      }
    }
  , 100
  , 1
  );
}

compile: em++ --bind -o emscripten_keydown_sample.out.html -std=c++11 emscripten_keydown_sample.cxx