iterator-operations.html

<emu-clause id="sec-getasynciterator" aoid="GetAsyncIterator">
  <h1>GetAsyncIterator ( _obj_ )</h1>
  <p>The abstract operation GetAsyncIterator with argument _obj_ performs the following steps:</p>
  <emu-alg>
    1. Let _method_ be ? GetMethod(_obj_, @@asyncIterator).
    1. If _method_ is *undefined*, let *method* be ? GetMethod(_obj_, @@iterator).
    1. Let _iterator_ be ? Call(_method_, _obj_).
    1. If Type(_iterator_) is not Object, throw a *TypeError* exception.
    1. Return _iterator_.
  </emu-alg>
</emu-clause>

<emu-clause id="sec-iteratorclose" aoid="IteratorClose">
  <h1>IteratorClose( _iterator_, _completion_, _iteratorKind_ )</h1>
  <p>The abstract operation IteratorClose with arguments _iterator_ and _completion_ and optional argument _iteratorKind_ is used to notify an iterator that it should perform any actions it would normally perform when it has reached its completed state.  The value of _iteratorKind_ is either ~normal~ or ~async~.</p>
  <emu-alg>
    1. Assert: Type(_iterator_) is Object.
    1. Assert: _completion_ is a Completion Record.
    1. If _iteratorKind_ was not passed, let _iteratorKind_ be ~normal~.
    1. Let _return_ be ? GetMethod(_iterator_, `"return"`).
    1. If _return_ is *undefined*, then
      1. Return Completion(_completion_).
    1. Let _innerResult_ be Call(_return_, _iterator_, « »).
    1. If _innerResult_ is not an abrupt completion and _iteratorKind_ is ~async~, then
      1. Let _innerResult_ be AwaitIterResultObject(_innerResult_).
    1. If _completion_.[[type]] is ~throw~, return Completion(_completion_).
    1. If _innerResult_.[[type]] is ~throw~, return Completion(_innerResult_).
    1. If Type(_innerResult_.[[value]]) is not Object, throw a *TypeError* exception.
    1. Return Completion(_completion_).
  </emu-alg>
</emu-clause>

<emu-clause id="sec-awaititerresultobject" aoid="AwaitIterResultObject">
  <h1>AwaitIterResultObject ( _asyncResult_ )</h1>
  <emu-alg>
    1. Let _result_ be ? AsyncFunctionAwait(_asyncResult_).
    1. Let _value_ be ? IteratorValue(_result_).
    1. If Type(_value_) is Object, then
      1. If ? IsCallable(? Get(_value_, `"then"`)) is *true*, then
        1. Let _done_ be ? IteratorComplete(_result_).
        1. Let _value_ be ? AsyncFunctionAwait(_value_).
        1. Let _result_ be CreateIterResultObject(_value_, _done_).
    1. Return _result_.
  </emu-alg>
</emu-clause>