Submitted answer is passed using standard sessionStorage. You can find the minimal code for typing and error comparison here (also in the Basic Note Type provided by the add-on).
I don’t really understand the second part of your question. If you are referring to the switch between displaying the question form and extra info on the backside, this is done by putting each layout in a respective container, which in turn are assigned display: none to leave only one on the screen at a time.