function swymCallbackFn() {    
    var wishlistButton = document.querySelector(".wishlist-btn");
    var wishlistHeart = document.querySelector("#wishlist-heart");
    
    // fetch all wishlist events
    if(wishlistButton) { _swat.fetchWrtEventTypeET(fetchCallbackFn, 4); }
  
    function updateButtonState({ makeDisabled = false } = {}) {
      wishlistHeart.firstElementChild.style.fill = "red";
      wishlistHeart.firstElementChild.style.stroke = "none";
      wishlistButton.lastElementChild.innerHTML = "Saved";
      
      if (makeDisabled) wishlistButton.setAttribute("disabled", true);
    }
  
    function fetchCallbackFn(products) {
      var activeProductId = SwymPageData.empi, 
          activeVariantId = SwymPageData.epi;

      var isInWishlist = products.find(function(p){
        return p.empi == activeProductId && p.epi == activeVariantId;
      });

      if(isInWishlist) { // update button status; item is in users wishlist
        updateButtonState({makeDisabled: true});
      } else {
        // register a click listener to update btn and add item to wishlist
        wishlistButton.addEventListener("click", function(e){
          if (SwymPageData) {

            SwymPageData.et = 4;	// et 4 stands for wishlist event type

            _swat.addToWishList(SwymPageData, function(e){
                updateButtonState();
            });
          }
        });
      }
    }
  }

  if (!window.SwymCallbacks) { window.SwymCallbacks = []; }

  window.SwymCallbacks.push(swymCallbackFn);