Combine local JS.

’yui-compressor’ is no longer used.

assets/js/_commons/back-to-top.js

@@ -0,0 +1,18 @@
+/*
+Reference: https://bootsnipp.com/snippets/featured/link-to-top-page
+*/
+$(window).scroll(function() {
+  if ($(this).scrollTop() > 50
+      && $('#sidebar-trigger').css('display') == 'none') {
+    $('#back-to-top').fadeIn();
+  } else {
+    $('#back-to-top').fadeOut();
+  }
+});
+
+$(function() {
+  $('#back-to-top').click(function() {
+    $('body,html').animate({scrollTop: 0}, 800);
+    return false;
+  });
+});