I can see this being useful for the same reason that it's useful that non-async functions in JavaScript can't be interrupted - it's as if you held a lock for th

I can see this being useful for the same reason that it's useful that non-async functions in JavaScript can't be interrupted - it's as if you held a lock for the entire function call. Between any two event handlers, anything could change. Similarly for await calls in JavaScript. And to get true parallelism, you need to start a separate worker. Concurrency issues can still happen, but not in low-level operations that don't do I/O. I don't see anything wrong with mutating a local variable in cases when it's purely a local effect. It's sometimes cleaner, since you can't accidentally refer to an obsolete version of a variable after mutating it.