You can have your Web App (or other in5 project) return to the last viewed page when your viewers re-open it.
To so so, save the following code into a plain text file with a .js extension:
useBookmark = true;
You can then attach this code to your output using the Resources section of the in5 export dialog.
Your output will then automatically store the last view page, and re-open on that page (for instance when the Web App is launched from the Home Screen, or the site is visited in the same browser).