HTML5 Callbacks and C++

I am trying to make a simple c++ class that wraps an HTML element. When the user clicks on the element, the onclick event would call a member function of the class. Perhaps I missed the obvious, but there doesn't seem to be any direct way to do that. I was able to use:
`emscripten_set_click_callback( "#button", this, 1, Button::on_button_click );`

However that required adding a static member function (on_button_click), which would then call the member function. I noticed that the callback has eventType as the first argument and was thinking that if userData was first instead, that would be ideal for member functions (provided userData = this).