I agree with Katana's comment. Anything after your redirect statement will not run because the page itself is redirecting. One way that I would suggest to still get the item_id and get around that barrier, would be to include the item_id in the redirect url as a parameter. Then once on the new page, parse that parameter out of the url and save the item_id. 
A great example from Cory Laviska's article on Parsing URLs in Javascript, shows how you can get the individual parameters from a URL. 
Building onto Manish' answer: 
Function on the current page:
function encode(item_id){
    $('.js-encode').click(function(){
    var url = $(this).data('url');
    location.href = url+'?saved_item_id='+item_id; // new url
    });
}
Function on the REDIRECTED Page (assuming you only have one parameter)
$( document ).ready(function() {
     var url = $(this).data('url');
     var item_id = url.queryKey['saved_item_id'];
     save(item_id);
 });
It may need a few tweeks because I didn't test the code, but hopefully it'll get you on the right track. :)
Hopefully this helps. If it helps and/or answers your question, please select as answer and up vote! :D Feel free to let me know if you have any questions