DOM manipulation is not covered in this tutorial until four chapters later, in Part 2. From the comments, it looks like some are ready for it and some are not. I don't know if the async stuff could be explained well without using DOM examples, and I haven't looked at the DOM chapter much, so don't know if it requires stuff from Part 1 beyond Chapter 10, but maybe it could be moved up, or referenced, or some short primer or in-context explanations provided to get people unfamiliar with the subject through the async chapter.