🎨 Optimised infinite scroll (#503)

no issue
- removed jQuery usage
- use the `<link rel="next">` tag provided by Ghost to determine the next page to fetch

assets/js/infinitescroll.js

@@ -1,19 +1,78 @@
-/* global maxPages */
+/**
+ * Infinite Scroll
+ */
+
+(function(window, document) {
+    // next link element
+    var nextElement = document.querySelector('link[rel=next]');
+    if (!nextElement) return;
+
+    // post feed element
+    var feedElement = document.querySelector('.post-feed');
+    if (!feedElement) return;
 
-// Code snippet inspired by https://github.com/douglasrodrigues5/ghost-blog-infinite-scroll
-$(function ($) {
-    var currentPage = 1;
-    var pathname = window.location.pathname;
-    var $document = $(document);
-    var $result = $('.post-feed');
     var buffer = 300;
 
     var ticking = false;
-    var isLoading = false;
+    var loading = false;
 
     var lastScrollY = window.scrollY;
     var lastWindowHeight = window.innerHeight;
-    var lastDocumentHeight = $document.height();
+    var lastDocumentHeight = document.documentElement.scrollHeight;
+
+    function onPageLoad() {
+        if (this.status === 404) {
+            window.removeEventListener('scroll', onScroll);
+            window.removeEventListener('resize', onResize);
+            return;
+        }
+
+        // append contents
+        var postElements = this.response.querySelectorAll('.post-card');
+        postElements.forEach(function (item) {
+            feedElement.appendChild(item);
+        });
+
+        // set next link
+        var resNextElement = this.response.querySelector('link[rel=next]');
+        if (resNextElement) {
+            nextElement.href = resNextElement.href;
+        } else {
+            window.removeEventListener('scroll', onScroll);
+            window.removeEventListener('resize', onResize);
+        }
+
+        // sync status
+        lastDocumentHeight = document.documentElement.scrollHeight;
+        ticking = false;
+        loading = false;
+    }
+
+    function onUpdate() {
+        // return if already loading
+        if (loading) return;
+
+        // return if not scroll to the bottom
+        if (lastScrollY + lastWindowHeight <= lastDocumentHeight - buffer) {
+            ticking = false;
+            return;
+        }
+
+        loading = true;
+
+        var xhr = new window.XMLHttpRequest();
+        xhr.responseType = 'document';
+
+        xhr.addEventListener('load', onPageLoad);
+
+        xhr.open('GET', nextElement.href);
+        xhr.send(null);
+    }
+
+    function requestTick() {
+        ticking || window.requestAnimationFrame(onUpdate);
+        ticking = true;
+    }
 
     function onScroll() {
         lastScrollY = window.scrollY;
@@ -22,94 +81,12 @@ $(function ($) {
 
     function onResize() {
         lastWindowHeight = window.innerHeight;
-        lastDocumentHeight = $document.height();
+        lastDocumentHeight = document.documentElement.scrollHeight;
         requestTick();
     }
 
-    function requestTick() {
-        if (!ticking) {
-            requestAnimationFrame(infiniteScroll);
-        }
-        ticking = true;
-    }
-
-    function sanitizePathname(path) {
-        var paginationRegex = /(?:page\/)(\d)(?:\/)$/i;
-
-        // remove hash params from path
-        path = path.replace(/#(.*)$/g, '').replace('////g', '/');
-
-        // remove pagination from the path and replace the current pages
-        // with the actual requested page. E. g. `/page/3/` indicates that
-        // the user actually requested page 3, so we should request page 4
-        // next, unless it's the last page already.
-        if (path.match(paginationRegex)) {
-            currentPage = parseInt(path.match(paginationRegex)[1]);
-
-            path = path.replace(paginationRegex, '');
-        }
-
-        return path;
-    }
-
-    function infiniteScroll() {
-        // sanitize the pathname from possible pagination or hash params
-        pathname = sanitizePathname(pathname);
-
-        // return if already loading
-        if (isLoading) {
-            return;
-        }
-
-        // return if not scroll to the bottom
-        if (lastScrollY + lastWindowHeight <= lastDocumentHeight - buffer) {
-            ticking = false;
-            return;
-        }
-
-        /**
-        * maxPages is defined in default.hbs and is the value
-        * of the amount of pagination pages.
-        * If we reached the last page or are past it,
-        * we return and disable the listeners.
-        */
-        if (currentPage >= maxPages) {
-            window.removeEventListener('scroll', onScroll, {passive: true});
-            window.removeEventListener('resize', onResize);
-            return;
-        }
-
-        isLoading = true;
-
-        // next page
-        currentPage += 1;
-
-        // Load more
-        var nextPage = pathname + 'page/' + currentPage + '/';
-
-        $.get(nextPage, function (content) {
-            var parse = document.createRange().createContextualFragment(content);
-            var posts = parse.querySelectorAll('.post');
-            if (posts.length) {
-                [].forEach.call(posts, function (post) {
-                    $result[0].appendChild(post);
-                });
-            }
-        }).fail(function (xhr) {
-            // 404 indicates we've run out of pages
-            if (xhr.status === 404) {
-                window.removeEventListener('scroll', onScroll, {passive: true});
-                window.removeEventListener('resize', onResize);
-            }
-        }).always(function () {
-            lastDocumentHeight = $document.height();
-            isLoading = false;
-            ticking = false;
-        });
-    }
-
-    window.addEventListener('scroll', onScroll, {passive: true});
+    window.addEventListener('scroll', onScroll, { passive: true });
     window.addEventListener('resize', onResize);
 
-    infiniteScroll();
-});
+    requestTick();
+})(window, document);