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assets/js/infinite-scroll.js

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+/* eslint-env browser */
+
+/**
+ * Infinite Scroll
+ * Used on all pages where there is a list of posts (homepage, tag index, etc).
+ *
+ * When the page is scrolled to 300px from the bottom, the next page of posts
+ * is fetched by following the the <link rel="next" href="..."> that is output
+ * by {{ghost_head}}.
+ *
+ * The individual post items are extracted from the fetched pages by looking for
+ * a wrapper element with the class "post-card". Any found elements are appended
+ * to the element with the class "post-feed" in the currently viewed page.
+ */
+
+(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;
+    }
+
+    var buffer = 300;
+
+    var ticking = false;
+    var loading = false;
+
+    var lastScrollY = window.scrollY;
+    var lastWindowHeight = window.innerHeight;
+    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('article.post-card');
+        postElements.forEach(function (item) {
+            // document.importNode is important, without it the item's owner
+            // document will be different which can break resizing of
+            // `object-fit: cover` images in Safari
+            feedElement.appendChild(document.importNode(item, true));
+        });
+
+        // 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;
+        requestTick();
+    }
+
+    function onResize() {
+        lastWindowHeight = window.innerHeight;
+        lastDocumentHeight = document.documentElement.scrollHeight;
+        requestTick();
+    }
+
+    window.addEventListener('scroll', onScroll, {passive: true});
+    window.addEventListener('resize', onResize);
+
+    requestTick();
+})(window, document);