The Telegram web client uses all sorts of features and a reimplementation of React.

> The project incorporates lots of technologically advanced features, modern Web APIs and techniques: WebSockets, Web Workers and WebAssembly, multi-level caching and PWA, voice recording and media streaming, cryptography and raw binary data operations, optimistic and progressive interfaces, complicated CSS/Canvas/SVG animations, reactive data streams, and so much more.

https://github.com/Ajaxy/telegram-tt

The dev is pretty much a genius.