自定义元素 - Hello World

创建一个名为 <hello-world> 的新 HTML 标签，它将显示 Hello World!：

<script>
//define a class extending HTMLElement
class HelloWorld extends HTMLElement {
    connectedCallback () {
      this.innerHTML = 'Hello, World!'
    }
}

//register the new custom element
customElements.define( 'hello-world', HelloWorld )
</script>

<!-- make use the custom element -->
<hello-world></hello-world>