Function reconcileChildrenIterator

code/composition/public/app.js:9527–9670

(returnFiber, currentFirstChild, newChildrenIterable, expirationTime)

  }

  function reconcileChildrenIterator(returnFiber, currentFirstChild, newChildrenIterable, expirationTime) {
    // This is the same implementation as reconcileChildrenArray(),
    // but using the iterator instead.

    var iteratorFn = getIteratorFn(newChildrenIterable);
    !(typeof iteratorFn === 'function') ? invariant(false, 'An object is not an iterable. This error is likely caused by a bug in React. Please file an issue.') : void 0;

    {
      // Warn about using Maps as children
      if (typeof newChildrenIterable.entries === 'function') {
        var possibleMap = newChildrenIterable;
        if (possibleMap.entries === iteratorFn) {
          warning(didWarnAboutMaps, 'Using Maps as children is unsupported and will likely yield ' + 'unexpected results. Convert it to a sequence/iterable of keyed ' + 'ReactElements instead.%s', getCurrentFiberStackAddendum$2());
          didWarnAboutMaps = true;
        }
      }

      // First, validate keys.
      // We'll get a different iterator later for the main pass.
      var _newChildren = iteratorFn.call(newChildrenIterable);
      if (_newChildren) {
        var knownKeys = null;
        var _step = _newChildren.next();
        for (; !_step.done; _step = _newChildren.next()) {
          var child = _step.value;
          knownKeys = warnOnInvalidKey(child, knownKeys);
        }
      }
    }

    var newChildren = iteratorFn.call(newChildrenIterable);
    !(newChildren != null) ? invariant(false, 'An iterable object provided no iterator.') : void 0;

    var resultingFirstChild = null;
    var previousNewFiber = null;

    var oldFiber = currentFirstChild;
    var lastPlacedIndex = 0;
    var newIdx = 0;
    var nextOldFiber = null;

    var step = newChildren.next();
    for (; oldFiber !== null && !step.done; newIdx++, step = newChildren.next()) {
      if (oldFiber.index > newIdx) {
        nextOldFiber = oldFiber;
        oldFiber = null;
      } else {
        nextOldFiber = oldFiber.sibling;
      }
      var newFiber = updateSlot(returnFiber, oldFiber, step.value, expirationTime);
      if (newFiber === null) {
        // TODO: This breaks on empty slots like null children. That's
        // unfortunate because it triggers the slow path all the time. We need
        // a better way to communicate whether this was a miss or null,
        // boolean, undefined, etc.
        if (!oldFiber) {
          oldFiber = nextOldFiber;
        }