Исправления JS для случаев отсутствия разметки JS-компонентов

src/blocks/nouislider/nouislider.js

 document.addEventListener('DOMContentLoaded', function(){
 
+  if(document.getElementById('demo-nouislider')) {
+
     var demoNoUiSlider = document.getElementById('demo-nouislider');
     var demoNoUiSliderStartInput = document.getElementById('demo-nouislider-start');
     var demoNoUiSliderEndInput = document.getElementById('demo-nouislider-end');
@@ -27,4 +29,6 @@ document.addEventListener('DOMContentLoaded', function(){
       demoNoUiSlider.noUiSlider.set([this.value, null]);
     });
 
+  }
+
 });

src/blocks/swipe/swipe.js

 document.addEventListener('DOMContentLoaded', function(){
 
+  if(document.getElementById('swipe-demo')) {
+
     window.mySwipe = new Swipe(document.getElementById('swipe-demo'), {
       startSlide: 0,
       speed: 400,
@@ -15,4 +17,5 @@ document.addEventListener('DOMContentLoaded', function(){
     // включить видимость блока (по умолчанию скрыт)
     document.getElementById('swipe-demo').classList.add('swipe--enable');
 
+  }
 });

src/blocks/to-top/to-top.js

 document.addEventListener('DOMContentLoaded', function(){
 
-  document.querySelector('#to-top').addEventListener('click', function(e) {
+  if(document.getElementById('to-top')) {
+
+    document.getElementById('to-top').addEventListener('click', function(e) {
       e.preventDefault();
       var scroll = window.pageYOffset;
       var targetTop = 0;
@@ -22,10 +24,10 @@ document.addEventListener('DOMContentLoaded', function(){
 
     function visibilityToggle() {
       if(window.pageYOffset >= 500) {
-      document.querySelector('#to-top').classList.add('to-top--visible');
+        document.getElementById('to-top').classList.add('to-top--visible');
       }
       else {
-      document.querySelector('#to-top').classList.remove('to-top--visible');
+        document.getElementById('to-top').classList.remove('to-top--visible');
       }
     }
 
@@ -45,4 +47,6 @@ document.addEventListener('DOMContentLoaded', function(){
       });
     }
 
+  }
+
 });