Function placeChild

docs/external/js/react-dom.development.js:13644–13670

(newFiber, lastPlacedIndex, newIndex)

    }

    function placeChild(newFiber, lastPlacedIndex, newIndex) {
      newFiber.index = newIndex;

      if (!shouldTrackSideEffects) {
        // Noop.
        return lastPlacedIndex;
      }

      var current = newFiber.alternate;

      if (current !== null) {
        var oldIndex = current.index;

        if (oldIndex < lastPlacedIndex) {
          // This is a move.
          newFiber.effectTag = Placement;
          return lastPlacedIndex;
        } else {
          // This item can stay in place.
          return oldIndex;
        }
      } else {
        // This is an insertion.
        newFiber.effectTag = Placement;
        return lastPlacedIndex;
      }
    }

    function placeSingleChild(newFiber) {
      // This is simpler for the single child case. We only need to do a