show "back to top" only when needed

boday_it/static/js/base.js

@@ -33,6 +33,18 @@ var Cl = window.Cl || {};
         'lowerThan': 'boxShadow'
       });
     }
+    // custom functions "botsicode"
+    const backTop = document.querySelector('.list-inline .pull-right'),
+      bodyContainer = document.querySelector('body>div.container'),
+      shBackTop = function() {
+        if (backTop && bodyContainer) {
+          backTop.style.opacity = +(bodyContainer.offsetTop + bodyContainer.getBoundingClientRect().height > window.innerHeight);
+        }
+      };
+    $(window).resize(shBackTop);
+    $(window).scroll(shBackTop);
+    shBackTop();
+
   });
 
 })(jQuery);