extract-all-appids-you-dont-have-one-your-wishlist.js

/* 
GUIDE
install the extension https://chromewebstore.google.com/detail/disable-content-security/ieelmcmcagommplceebfedjlakkhpden
go to https://store.steampowered.com/ and activate the Browser extension 
Press F5 
Open the Console by pressing F12
paste the Code in to it
Press enter and wait
*/

(function() {
  var wishlist = [];

  // Fetch app list from GetAppList API
  jQuery.ajax({
    type: 'GET',
    url: '//api.steampowered.com/ISteamApps/GetAppList/v2',
    dataType: 'jsonp',
    success: function(result) {
      jQuery.each(result['applist']['apps'], function(key, value) {
        wishlist.push(value['appid']);
      });

      // Fetch wishlist from dynamicstore/userdata
      jQuery.ajax({
        type: 'GET',
        url: 'https://store.steampowered.com/dynamicstore/userdata/',
        dataType: 'json',
        success: function(result) {
          var wishlisted = result['rgWishlist'];

          // Compare wishlist with app list and log app IDs not on wishlist
          var newWishlist = wishlist.filter(function(appid) {
            return !wishlisted.includes(appid);
          });

          console.log(newWishlist.join(',')); // Log app IDs not on wishlist
        },
        error: function(httpReq, status, exception) {
          ShowAlertDialog('Failed to fetch wishlist data', 'Error: ' + status);
        }
      });
    },
    error: function(httpReq, status, exception) {
      ShowAlertDialog('Failed to fetch app list', 'Error: ' + status);
    },
    jsonp: 'jsonp'
  });
})();