This project is being continued as a commercial offering at SpaceAware.io. If you are curious about our progress, check out my profile on LinkedIn.
We used the open source Vallado C++ code available at Celestrak.org, and compiled it to WebAssembly.
Our plan is to let subscribers embed our version of Cesium with the built-in propagator on their own website, and when we are able, open source the WebAssembly propagation compiler pipeline and invite collaboration.
Until then, we would appreciate not reverse engineering our source and posting pieces of it online. The results will be inaccurate unless you reverse engineer the entire app, and currently the app / wasm binaries are proprietary and unlicensed for any use, commercial or private.