Design document are stored, manipulated, and rendered in WASM and WebGL. The surrounding UI (toolbar, properties panel, layers panel, etc) is written in React.

Design document are stored, manipulated, and rendered in WASM and WebGL. The surrounding UI (toolbar, properties panel, layers panel, etc) is written in React. It's done that way because documents can get really large and having more low-level memory management helps a lot there. On the other hand, writing UI in C++ is really tedious and React has served us great. For non-performance sensitive areas, I'd much rather use TypeScript + React, despite being comfortable writing C++. So obviously we're big fans on WASM, but we don't expect nor want JS/HTML/CSS to go away anytime soon.