If you need the user code to execute on the main thread, then unfortunately I am aware of none besides bundling your own tailored system. Pyret used to use its

If you need the user code to execute on the main thread, then unfortunately I am aware of none besides bundling your own tailored system. Pyret used to use its own runtime system [0] but Stopify was created in part to replace it due to the maintenance burden and complexity of "vanilla" JS interoperability. [0] https://www.pyret.org/docs/latest/s_running.html https://www.pyret.org/docs/latest/s_running.html