emscripten_set_mousedown_callback does not call the callback function

#include <emscripten.h>
#include <emscripten/html5.h>
#include <iostream>

int main()
{
    // Mouse Button Down:
    emscripten_set_mousedown_callback(
        EMSCRIPTEN_EVENT_TARGET_WINDOW, nullptr, 0, +[](int eventType,
        const EmscriptenMouseEvent *e, void *userData) -> EM_BOOL
        {
            std::cout << "Mouse down: " << e->button << "\n";
            return EM_FALSE;
        });
}