Define with customElements.define()

app.js

@@ -0,0 +1,5 @@
+import LazyloadImage from './lazyload-image.js';
+
+customElements.define('lazyload-image', LazyloadImage, {
+  extends: 'img'
+});

index.html

@@ -5,7 +5,8 @@
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <title>lazyload-image</title>
     <link rel="stylesheet" href="https://cdn.jsdelivr.net/highlight.js/9.3.0/styles/github.min.css">
-    <link rel="import" href="lazyload-image.html">
+    <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Roboto:400,700">
+    <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Roboto Mono:400,700">
     <style>
       body { font-family: Roboto, Helvetica, Arial, sans-serif; }
       code { font-family: "Roboto Mono", "Source Code Pro", Consolas, "Courier New", monospace; }
@@ -38,41 +39,46 @@ <h2>Install</h2>
 # via bower
 $ bower install lazyload-image</code></pre>
       <h2>Usage</h2>
-      <p>Load <code class="html">lazyload-image.html</code> in your HTML.</p>
-      <pre><code class="html">&lt;link rel="import" href="lazyload-image.html"&gt;</code></pre>
+      <p>Load <code class="html">lazyload-image.js</code> in your JavaScript.</p>
+      <pre><code class="javascript">import LazyloadImage from './lazyload-image.js';
+
+customElements.define('lazyload-image', LazyloadImage, {
+  extends: 'img'
+});</code></pre>
       <p>Modify your <code class="html">&lt;img&gt;</code> elements such as following.</p>
       <pre><code class="html">&lt;img is="lazyload-image" src="path/to/your/image.jpg" width="100" height="100"&gt;</code></pre>
       <p>You can specify load offset.</p>
       <pre><code class="html">&lt;img is="lazyload-image" src="path/to/your/image.jpg" offset="200" width="100" height="100"&gt;</code></pre>
       <h2>Fallback</h2>
-      <p>If browser does not support <code class="javascript">document.registerElement()</code>, Images will be loaded as usual.</p>
+      <p>If browser does not support <code class="javascript">customElements.define()</code>, Images will be loaded as usual.</p>
       <h2>Demo</h2>
       <p>Recommend you to open <strong>DevTools's Elements tab</strong> to see behavior of <code class="html">&lt;lazyload-image&gt;</code>.</p>
       <div class="image-container">
-        <img is="lazyload-image" offset="200" src="assets/img/1.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/2.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/3.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/4.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/5.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/6.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/7.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/8.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/9.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/10.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/11.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/12.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/13.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/14.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/15.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/16.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/17.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/18.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/19.jpg" width="100%">
-        <img is="lazyload-image" offset="200" src="assets/img/20.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/1.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/2.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/3.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/4.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/5.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/6.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/7.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/8.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/9.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/10.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/11.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/12.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/13.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/14.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/15.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/16.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/17.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/18.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/19.jpg" width="100%">
+        <img is="lazyload-image" offset="200px" src="assets/img/20.jpg" width="100%">
       </div>
     </div>
     <a href="https://github.com/1000ch/lazyload-image" class="github-corner"><svg width="80" height="80" viewbox="0 0 250 250" style="fill:#151513; color:#fff; position: absolute; top: 0; border: 0; right: 0;"><path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path><path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2" fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path><path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z" fill="currentColor" class="octo-body"></path></svg></a><style>.github-corner:hover .octo-arm{animation:octocat-wave 560ms ease-in-out}@keyframes octocat-wave{0%,100%{transform:rotate(0)}20%,60%{transform:rotate(-25deg)}40%,80%{transform:rotate(10deg)}}@media (max-width:500px){.github-corner:hover .octo-arm{animation:none}.github-corner .octo-arm{animation:octocat-wave 560ms ease-in-out}}</style>
     <script src="https://cdn.jsdelivr.net/highlight.js/9.3.0/highlight.min.js"></script>
     <script>hljs.initHighlightingOnLoad();</script>
+    <script type="module" src="app.js"></script>
   </body>
 </html>

lazyload-image.js

@@ -0,0 +1,84 @@
+export default class LazyloadImage extends HTMLImageElement {
+  static get FALLBACK_IMAGE() {
+    return 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAEElEQVR42gEFAPr/AP///wAI/AL+Sr4t6gAAAABJRU5ErkJggg==';
+  }
+
+  static get observedAttributes() {
+    return [
+      'offset'
+    ];
+  }
+
+  constructor(width, height) {
+    super(width, height);
+
+    this.original = this.currentSrc || this.src;
+    this.src = LazyloadImage.FALLBACK_IMAGE;
+    this.onIntersect = this.onIntersect.bind(this);
+  }
+
+  connectedCallback() {
+    this.observe();
+  }
+
+  disconnectedCallback() {
+    this.unobserve();
+  }
+
+  get offset() {
+    return this.getAttribute('offset');
+  }
+
+  set offset(value) {
+    this.setAttribute('offset', value);
+  }
+
+  get observer() {
+    if (!this.intersectionObserver) {
+      this.intersectionObserver = new IntersectionObserver(this.onIntersect, {
+        rootMargin: this.offset
+      });
+    }
+
+    return this.intersectionObserver;
+  }
+
+  observe() {
+    this.observer.observe(this);
+  }
+
+  unobserve() {
+    this.observer.unobserve(this);
+    this.observer.disconnect();
+  }
+
+  onIntersect(entries) {
+    if (entries.length === 0) {
+      return;
+    }
+
+    if (entries[0].intersectionRatio <= 0) {
+      return;
+    }
+
+    this.addEventListener('load', () => {
+      this.unobserve();
+    });
+
+    this.addEventListener('error', () => {
+      this.src = LazyloadImage.FALLBACK_IMAGE;
+      this.unobserve();
+    });
+
+    this.src = this.original;
+  }
+
+  attributeChangedCallback(name, oldValue, newValue) {
+    if (this.observer === null) {
+      return;
+    }
+
+    this.unobserve();
+    this.observe();
+  }
+}

readme.md

@@ -20,21 +20,30 @@ $ bower install lazyload-image
 
 ## Usage
 
-Load `lazyload-image.html` in your HTML.
+Load `lazyload-image.js` in your JavaScript.
 
-```html
-<link rel="import" href="lazyload-image.html">
+```javascript
+import LazyloadImage from './lazyload-image.js';
+
+customElements.define('lazyload-image', LazyloadImage, {
+  extends: 'img'
+});
 ```
 
 Modify your `<img>` elements such as following.
 
 ```html
-<img is="lazyload-image" src="path/to/your/image.jpg" offset="200" width="100" height="100">
+<img 
+  is="lazyload-image" 
+  src="path/to/your/image.jpg" 
+  offset="200px" 
+  width="100" 
+  height="100">
 ```
 
 ## Fallback
 
-If a browser does not support `document.registerElement()`, images will be loaded as usual.
+If a browser does not support `customElements.define()`, images will be loaded as usual.
 
 ## License