TCO is something that specific JS engines need to implement. It is implemented in JSC (Safari), but not in V8 or SpiderMonkey. Also see https://v8.dev/blog/mode

TCO is something that specific JS engines need to implement. It is implemented in JSC (Safari), but not in V8 or SpiderMonkey. Also see https://v8.dev/blog/modern-javascript#proper-tail-calls https://v8.dev/blog/modern-javascript#proper-tail-calls. As this is an engine feature rather than a spec thing, there is nothing me (or any other TC39 delegate) can do.