如何代理自定义元素(Web组件)

Question

class A extends HTMLElement {
  constructor() {
    super()
    return new Proxy(this, {})
  }
}

window.customElements.define('a-element', A)

<a-element></a-element>

我如何代理自定义元素？

当我尝试它:

Uncaught InvalidStateError: custom element constructors must call super() first and must not return a different object.

Answer 1

您可以Proxify 类或自定义元素的实例.

给定以下自定义元素定义:

class A extends HTMLElement {
  constructor() {
    super()
  }
  connectedCallback() {
    this.innerHTML = 'Hello'    
  }
}
customElements.define( 'a-element', A )

自定义元素实例的代理

从实例引用创建代理(此处:) ae:

<a-element id="ae"></a-element>
<script>
  var b1 = new Proxy( ae, {
    get ( target, value ) { return target[value] }       
  } )
  console.log( b1.innerHTML ) // => "Hello"
</script>

自定义元素类的代理

定义construct陷阱以捕获new运算符:

<script>
  var B = new Proxy( A, {
    construct() { return new A }
  } )
  var b2 = new B
  document.body.appendChild( b2 )
  console.log( b2.innerHTML ) // => "Hello"
</script>

从类Proxy获取自定义元素实例代理

如果要实例化自定义元素并直接获取一个代理对象,可以将上述两种解决方案结合起来.

以下示例显示如何获取<a-element>将在控制台中登录每个属性访问权限的元素的代理.construct()类Proxy中定义的陷阱返回自身为实例化自定义元素的代理.

class A extends HTMLElement {
  constructor() {
    super()
  }
  connectedCallback() {
    this.innerHTML = 'Hello'    
  }
}
customElements.define( 'a-element', A )		

var P = new Proxy( A, {
  construct () { 
    return new Proxy ( new A, {
      get ( target, value ) { 
        if ( value == 'element' ) 
          return target
        console.info( `proxy: property ${value} for <${target.localName}> is "${target[value]}"` )
        return target[value]
      }       
    } )
  }
} )
var p = new P
document.body.appendChild( p.element )
console.log( p.innerHTML )