usage of jump.js for the smooth scrolling

package.json

@@ -30,6 +30,7 @@
   ],
   "homepage": "https://github.com/FriendsOfTrowel/Covers#readme",
   "dependencies": {
+    "jump.js": "^1.0.2",
     "trowel-core": "^4.0.2"
   },
   "devDependencies": {

src/javascript/covers.js

@@ -1,3 +1,6 @@
+import jump from '../../node_modules/jump.js';
+
+
 export default class TrowelCovers {
   constructor(elements, options = {}) {
     [].slice.call(elements).forEach(function(element, index) {
@@ -18,7 +21,7 @@ class TrowelCover {
   _setOptions(customOptions) {
     const defaultOptions = {
       scrollDuration: 500,
-      topOffset: 0,
+      offset: 0,
     };
 
     let options = {};
@@ -38,8 +41,10 @@ class TrowelCover {
   }
 
   scrollDown() {
-    const scrollTop = this.element.offsetTop + this.element.offsetHeight - this.options.topOffset;
-    return this._smoothScrollTo(document.body, scrollTop, this.options.scrollDuration);
+    const scrollTop = this.element.offsetTop + this.element.offsetHeight + this.options.offset;
+    return jump(scrollTop, {
+      duration: this.options.scrollDuration,
+    });
   }
 
   _smoothScrollTo(element, target, duration) {

test/src/index.html.twig

@@ -36,7 +36,9 @@
 
     <script src="./javascript/covers.js"></script>
     <script type="text/javascript">
-        var covers = new TrowelCovers(document.querySelectorAll('.cover'));
+        var covers = new TrowelCovers(document.querySelectorAll('.cover'), {
+            offset: -100,
+        });
     </script>
   </body>
 </html>

yarn.lock

@@ -2494,6 +2494,10 @@ jsprim@^1.2.2:
     json-schema "0.2.3"
     verror "1.3.6"
 
+jump.js:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/jump.js/-/jump.js-1.0.2.tgz#e0641b47f40a38f2139c25fda0500bf28e43015a"
+
 kind-of@^3.0.2:
   version "3.2.0"
   resolved "https://registry.yarnpkg.com/kind-of/-/kind-of-3.2.0.tgz#b58abe4d5c044ad33726a8c1525b48cf891bff07"