I'm looking at a situation that requires a fair bit of data storage that I have considered using sessionScope variables for. In a small test that I ran this worked well, but the data does get written back to the server with each change to the data. I'm considering creating a JAVA bean to update and control the structure of this data and store it in a series of sessionStorage variables. The sessionStorage is easy in CSJS but I'm not sure how to access these variables from a JAVA Bean. 
The application is something like a shopping cart so I would maintain the data in the sessionStorage until the document submit, then load the values into the document and save it and I think this would work best as a JAVA.