I have a ASP web application that uses listboxes. My dilemma is that changes in items selection on the listboxes will happen fast and frequently, so doing a postback to get the information that I need would end up being very slow on the client side.

My question is: 
What is the best way to store data on the client side? or should I just use something like Postback, or ajax?

The information that needs to be stored could be in a single string for each item that I can split, but there will need to be the information for all of the items in the Listbox and the number of items in the Listbox is unknown.

Please let me know what you think would be the best place to have the information.