wip(js): add head.html and assets/js

assets/js/modules/components/img-loading.js

@@ -0,0 +1,67 @@
+/**
+ * Setting up image lazy loading and LQIP switching
+ */
+
+const ATTR_DATA_SRC = 'data-src';
+const ATTR_DATA_LQIP = 'data-lqip';
+
+const cover = {
+  SHIMMER: 'shimmer',
+  BLUR: 'blur'
+};
+
+function removeCover(clzss) {
+  this.parentElement.classList.remove(clzss);
+}
+
+function handleImage() {
+  if (!this.complete) {
+    return;
+  }
+
+  if (this.hasAttribute(ATTR_DATA_LQIP)) {
+    removeCover.call(this, cover.BLUR);
+  } else {
+    removeCover.call(this, cover.SHIMMER);
+  }
+}
+
+/**
+ * Switches the LQIP with the real image URL.
+ */
+function switchLQIP() {
+  const src = this.getAttribute(ATTR_DATA_SRC);
+  this.setAttribute('src', encodeURI(src));
+  this.removeAttribute(ATTR_DATA_SRC);
+}
+
+export function loadImg() {
+  const images = document.querySelectorAll('article img');
+
+  if (images.length === 0) {
+    return;
+  }
+
+  images.forEach((img) => {
+    img.addEventListener('load', handleImage);
+  });
+
+  // Images loaded from the browser cache do not trigger the 'load' event
+  document.querySelectorAll('article img[loading="lazy"]').forEach((img) => {
+    if (img.complete) {
+      removeCover.call(img, cover.SHIMMER);
+    }
+  });
+
+  // LQIPs set by the data URI or WebP will not trigger the 'load' event,
+  // so manually convert the URI to the URL of a high-resolution image.
+  const lqips = document.querySelectorAll(
+    `article img[${ATTR_DATA_LQIP}="true"]`
+  );
+
+  if (lqips.length) {
+    lqips.forEach((lqip) => {
+      switchLQIP.call(lqip);
+    });
+  }
+}