// Function to be reference by C/C++ via function pointer
function func() {
    console.log("Hello world")
    return 3;
}

// Cannot register functions until Emscripten is initialized
Module.onRuntimeInitialized = function()
{
    // Get memory address of func()
    var funcPtr = addFunction(func, 'v');

    // Invoke C method that calls function pointer
    Module._callFuncPtr(funcPtr);
};