Can I get the code to die()?

As I do not use too much javascript I was wondering how one might go about doing a confirmation box to help eliminate duplicates. For example:
I have a bill entered into the db. I can check for a duplicate before adding a duplicate record. Right now the confirmation comes up but I am not sure how to get javascript to return to the page of code and implement further PHP.
Are vars in javascript accessible in PHP? Can I get the code to die()?

Thanks in Advance

two ways to approach this:

1. use ajax to detect the duplicate and then pop up a js confirm box

2. process the item as normal, run your normal detection and then present both items if a duplicate is suspected and let the user select one with a radio button
once the approach is decided a strategy can be developed in how to show the info for a confirmation