Function placeChild

lib/assets/react-source/development/react.js:17204–17230

(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