iterator-operations.html

<emu-clause id="sec-getiterator" aoid="GetIterator">
  <h1>GetIterator ( _obj_ <ins>[ , _hint_ ]</ins>[ , _method_ ] )</h1>
  <emu-note type="editor">
    <p>This abstract operation has been modified to accept an optional parameter _hint_ which indicates whether we should attempt to find an async iterator for the object. Existing call sites which use the optional _method_ parameter (`Array.from` and IterableToArrayLike) must be updated to pass the ~normal~ hint.</p>
  </emu-note>
  <p>The abstract operation GetIterator with argument _obj_ and optional arguments _hint_ and _method_ performs the following steps:</p>
  <emu-alg>
    1. <ins>If _hint_ was not passed, let _hint_ be ~normal~.</ins>
    1. If _method_ is not present, then
      1. <del>Set _method_ to ? GetMethod(_obj_, @@iterator).</del>
      1. <ins>If _hint_ is ~async~,</ins>
        1. <ins>Set _method_ to ? GetMethod(_obj_, @@asyncIterator).</ins>
        1. <ins>If _method_ is *undefined*,
          1. <ins>Let _syncMethod_ be ? GetMethod(_obj_, @@iterator).</ins>
          1. <ins>Let _syncIteratorRecord_ be ? GetIterator(_obj_, ~normal~, _syncMethod_).</ins>
          1. <ins>Return ? CreateAsyncFromSyncIterator(_syncIteratorRecord_).</ins>
      1. <ins>Otherwise, set _method_ to ? GetMethod(_obj_, @@iterator).</ins>
    1. Let _iterator_ be ? Call(_method_, _obj_).
    1. If Type(_iterator_) is not Object, throw a *TypeError* exception.
    1. Let _nextMethod_ be ? GetV(_iterator_, `"next"`).
    1. Let _iteratorRecord_ be Record {[[Iterator]]: _iterator_, [[NextMethod]]: _nextMethod_, [[Done]]: *false*}.
    1. Return _iteratorRecord_.
  </emu-alg>
</emu-clause>

<emu-clause id="sec-asynciteratorclose" aoid="AsyncIteratorClose">
  <h1><ins>AsyncIteratorClose ( _iteratorRecord_, _completion_ )</ins></h1>
  <p>The abstract operation AsyncIteratorClose with arguments _iteratorRecord_ and _completion_ is used to notify an async iterator that it should perform any actions it would normally perform when it has reached its completed state:</p>
  <emu-alg>
    1. Assert: Type(_iteratorRecord_.[[Iterator]]) is Object.
    1. Assert: _completion_ is a Completion Record.
    1. Let _iterator_ be _iteratorRecord_.[[Iterator]].
    1. Let _return_ be ? GetMethod(_iterator_, `"return"`).
    1. If _return_ is *undefined*, return Completion(_completion_).
    1. Let _innerResult_ be Call(_return_, _iterator_, &laquo; &raquo;).
    1. If _innerResult_.[[Type]] is ~normal~, set _innerResult_ to Await(_innerResult_.[[Value]]).
    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>