如何在客户端存储用户名列表？

I have a load of chat boxes which come up on click of a username within a list. The problem is I need to know which are currently chosen to hide/show if more are clicked than there is screen space (think of facebook - you keep clicking friends for private message and when no more fit along the bottom, the next one takes the last boxes spot. Clearly you hide this last one, but want it to come back if you close this current choice)I have a load of chat boxes which come up on cl