Accessing session related data while using full page caching (e.g. getting current user wishlist items)

Hi All,

I’m just wondering if anyone else has ran into headaches related to full page caching for seemingly trivial coding. One example would be, in a custom theme, code to check to see if an item in a listing is in a user’s wishlist. If so, perhaps change the icon/color, etc. Or perhaps adding some simple ajax functionality to add an item quickly to a wishlist. I know there are many plugins, some free, that do such things, but they don’t seem to work (or work well) with full page caching enabled, using Varnish, or some other. The issue appears to be with accessing any user session related data in a way that doesn’t break caching.

There are some dribbles of resources out there, on Stackoverflow etc., that allude to various ways to deal with this, but I haven’t been able to really put something together that works well, without going down several other rabbit-holes. Is there some very simplistic solution to this that someone could point me towards?

Much appreciated, as always.