With 'modern C++' you can make APIs way nicer than the Java-like API going on here. Lambdas really help, along with RAII which has already been around. I have an API going where the following syntax creates a div with a 'toolbar' class and a toggle button with the 'edit' class and updates the DOM (C++ running in WASM, using IncrementalDOM for the DOM access):

  ui.div()("toolbar")([&]() {
    ui.button()("edit")("selected", editing)("click", [&](emscripten::val target) {
      editing = !editing;
    });
  });

This works by having `.div()` etc. return an `Elem` type whose constructor opens an HTML element and destructor closes it, with various overloads of `operator()` letting you set attributes, bind events or add child elements.

Here's a video of some results with C++ and CSS: https://twitter.com/snikhilesh/status/1279913032471031809

I should do a writeup about this soon...