Example of how to deal with HTML elements and callbacks entirely in Emscripten/C++.

example.cpp

/* 
  I know I pieced this together largely from another person's idea and their goal of trying to deal with 
  XMLHTTPRequests. I unfortunately can't find the original source, if you happen to be that person and this looks 
  familiar, link me to your post(s) and I'll credit you properly
 */


// Somewhere in your .cpp file "EmscriptenCallback" and "Callback" can be whatever you want, it just has to be a unique name
// for the argument to the std::function, that can be whatever you want too but for the purposes of this i think it makes sense to 
// leave it as a val since you're expecting an event object back.
EMSCRIPTEN_BINDINGS( EmscriptenCallback ) {
  emscripten::class_<std::function<void( emscripten::val e )> >( "Callback" )
	.constructor<>()
	.function( "onload", &std::function<void( emscripten::val e )>::operator());
};


auto fun = emscripten::val( onDrop )[ "onload" ].call<emscripten::val>( "bind", emscripten::val(<your std::function>) );

// imagine this is already assigned to an element on the DOM
emscripten::val el;
 
// call set with the event name and your function.
el.set( "ondrop" , fun);