A script for Ecwid to display the 'Preorder' label instead of 'In stock' when a product has unlimited stock quantity

ecwid_preorder_for_unlimited_stock.html

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js"></script>
<script>
if (typeof(Ecwid) == 'object') {
  Ecwid.OnAPILoaded.add(function() {
    var preorderLabel = "Preorder";   

    function checkPreorder() {
      if (
        !jQuery(".ecwid-productBrowser-details-qtyAvailInfo").is(':visible')
        && jQuery(".ecwid-productBrowser-details-outOfStockLabel").length == 0
      ) {         
          // The item's stock quantity is unlimited, let's show preorder label
          jQuery('.ecwid-productBrowser-details-inStockLabel').first().text(preorderLabel);
      }
    }    

    Ecwid.OnPageLoaded.add(function(page) {
      if ('PRODUCT' == page.type) {
        checkPreorder();
        
        jQuery('.ecwid-productBrowser-details-optionsPanel input[type=radio]').each(function() {
          jQuery(this).click(function() {
            setTimeout(checkPreorder, 500);
          });
        });

        jQuery('.ecwid-productBrowser-details-optionsPanel select').each(function() {
          jQuery(this).change(function() {
            setTimeout(checkPreorder, 500);
          });
        });
      }
    });
  });
}
</script>

This is probably a stupid question but where do you paste the code?