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Chris Tate
120c65bfbb
JavaScript reads an iterator's `next` when the iterator opens and keeps calling that function, so a `next` the iterator assigns while it runs is not called. The for-of loop and the spread drain over an object-literal iterator read the field on every step; they now read it once after the open (classIteratorNextRead) and call the function they read. The checked-dynamic spread drain (%iterator.pack.checked) does the same, using the stepping the for-of and Array.from drains already use. `for await` over a synchronous iterator closes it on an early exit the way the async-from-sync iterator does: return()'s result is read for done and value, and the value is awaited, so a pending promise settles before the loop continues and a rejected one rejects the loop (after a throw from the body, the body's error still wins).