[taralx]

Why is that a race? IIRC Promise.then is supposed to invoke the callback immediately (or on next loop) if the promise is already resolved.

[Mitranim]

It would be race-free if `.then()` was invoked synchronously when evaluating the `await` expression, just like in normal Promise-based code. Currently in V8, there's a delay between evaluating `await` and actually calling `.then()`. If the promise uses a sufficiently nimble scheduler (i.e. based on `process.nextTick`), its unhandled rejection handler may run _in between_, throwing an exception, polluting stderr and possibly killing the process.

Example with Posterus:

  async function main() {
    try {
      await Future.fromError('fail')
    }
    catch (err) {
      console.error('caught:', err)
    }
  }

In Node, this actually produces an unhandled rejection because Posterus's scheduler uses `process.nextTick` and squeezes into this unnecessary delay. Doesn't happen if you `.catch()` manually or just use Posterus coroutines instead of interoping with async/await, but it highlights the incorrect implementation of async/await in the first place. (Or is the spec at fault?)