for ... of

for...of statement rely on iterator.

During compilation, the for...of statement is expanded using an iterator.

for (const value of myIterable) {
}

is equivalent to

for (
  let it: MyIterator = myIterable[Symbol.iterator](), ret: IteratorResult<string> = it.next();
  !ret.done;
  ret = it.next()
) {
  const value = it.value;
}