PHP/Java script: how to keep selected value after posting?

The short version of my answer is "hidden form fields". You can p a value through a long series of pages/scripts that way. Get the value using $_POST or $_GET and put it in the form as a hidden field if it's not going to be used in any of the displayed fields for that step of the process. When you finally get to step 100 or whatever you still have the value entered way back when.