Save a copy of offline application

I use an online application, it has a feature that if I went offline it keeps working and by the time I connect the internet again it synchronize all data which edited offline. So, I am wondering if I can get a copy of this application (like saving the webpage) so it includes all things needed for it to work offline, so I do not need to load the first page of it to start working. It is similar to if I loaded the page then turned the internet off.

Thanks in advance.