if you write harder concurrent program in JS, single threaded event loop does not help. It still has also same concurrency problems. e.g. if there is shared glo

if you write harder concurrent program in JS, single threaded event loop does not help. It still has also same concurrency problems. e.g. if there is shared global mutable state: a) in workflow 1 you have, do_some_work_on_global_state; do some IO; in IO callback, finish more do_some_work_on_global_state. b) in workflow 2 .. same like above work on global_state. Now, in IO callback, you don't know if workflow 2 ran and have to handle all possible combinations of global_state above. Replace global_state with common_state and problem still remains. If you don't have common_state between multiple workflows, then it is not a hard concurrency problem and should be easy to do in all languages.