AJAX + PHP store array of previous commands(repost)

I have a website frontend, coded in Javascript with AJAX. When the user issues a command (e.g. clicks a button), the frontend Javascript communicates using a PHP XML-RPC client to an XML-RPC server on the backend. The backend does some processing and returns a response. I would like the frontend to keep track of the last 12 commands issued. However, if the "Start over" button is clicked, this list of commands should be cleared. This list should be passed to the XML-RPC server.