1 files changed, 54 insertions, 0 deletions
diff --git a/src/static/js/lazy-loading.js b/src/static/js/lazy-loading.js
new file mode 100644
index 00000000..1df56f08
--- /dev/null
+++ b/src/static/js/lazy-loading.js
@@ -0,0 +1,54 @@
+/* eslint-env browser */
+
+// Lazy loading! Roll your own. Woot.
+// This file includes a 8unch of fall8acks and stuff like that, and is written
+// with fairly Olden JavaScript(TM), so as to work on pretty much any 8rowser
+// with JS ena8led. (If it's disa8led, there are gener8ted <noscript> tags to
+// work there.)
+
+var observer;
+
+function loadImage(image) {
+  image.src = image.dataset.original;
+}
+
+function lazyLoad(elements) {
+  for (var i = 0; i < elements.length; i++) {
+    var item = elements[i];
+    if (item.intersectionRatio > 0) {
+      observer.unobserve(item.target);
+      loadImage(item.target);
+    }
+  }
+}
+
+function lazyLoadMain() {
+  // This is a live HTMLCollection! We can't iter8te over it normally 'cuz
+  // we'd 8e mutating its value just 8y interacting with the DOM elements it
+  // contains. A while loop works just fine, even though you'd think reading
+  // over this code that this would 8e an infinitely hanging loop. It isn't!
+  var elements = document.getElementsByClassName('js-hide');
+  while (elements.length) {
+    elements[0].classList.remove('js-hide');
+  }
+
+  var lazyElements = document.getElementsByClassName('lazy');
+  var i;
+  if (window.IntersectionObserver) {
+    observer = new IntersectionObserver(lazyLoad, {
+      rootMargin: '200px',
+      threshold: 0,
+    });
+    for (i = 0; i < lazyElements.length; i++) {
+      observer.observe(lazyElements[i]);
+    }
+  } else {
+    for (i = 0; i < lazyElements.length; i++) {
+      var element = lazyElements[i];
+      var original = element.getAttribute('data-original');
+      element.setAttribute('src', original);
+    }
+  }
+}
+
+document.addEventListener('DOMContentLoaded', lazyLoadMain);