WebComponents：Firefox 自定义元素未显示

Question

我正在使用网络组件 "custom elements" 功能并且需要支持旧浏览器（Firefox v60），因此不是通过加载所有 polyfill 的 webcomponent-loader.js 加载 polyfill。基于特征检测的延迟加载自定义元素 polyfill

(function() {
if(!window.customElements){
var ce = document.createElement('script');
ce.type = 'text/javascript';
ce.async = true;
ce.src = 'https://unpkg.com/@webcomponents/custom-elements@1.2.4/custom-elements.min.js';
/**

     * loading "customElement" polyfills wont't fire "WebComponentsReady" event, it will be called when we use
     * "webcomponent-loader.js" but it will load other polyfills("shadow-dom"), so loading the "customElements" polyfill alone
     * based on feature detection and firing "WebComponentsReady" event manually.
     */
  ce.onload = function() {
      document.dispatchEvent(
          new CustomEvent('WebComponentsReady', {bubbles: true}));
  };
  var st = document.getElementsByTagName('script')[0];
  st.parentNode.insertBefore(ce, st);
}
})()

并在加载时手动触发 WebComponentsReady 事件。注册元素如下

let registerElement = () => {
 if(!window.customElements.get(“wc-button")){
   window.customElements.define(‘wc-button', WCButton);
 }
};

if(window.customElements){
  registerElement();
 } else {
  document.addEventListener('WebComponentsReady', registerElement);
}

WebComponentsReady 已触发，并且已在侦听器回调中调用 define/register 元素，但元素未在 firefox60.6.1esr（64 位）的页面中显示或加载

Answer 1

webcomponents-loader.js 为你做特征检测您不必等待 WebComponentsReady 事件，而是

<script src="https://unpkg.com/@webcomponents/webcomponentsjs/webcomponents-loader.js"></script>
<script>
window.WebComponents.waitFor(() => {
   // do stuff that needs the polyfill
})
</script>

更多信息：

Answer 2

HTMLElement 只能在实现自定义元素时进行扩展（使用 polyfill 本机实现）。

因此，您必须仅在加载 polyfill 后定义 <wc-button> 自定义元素 class。

在你的例子中：

let registerElement = () => {
    if(!window.customElements.get("wc-button")){
         //define the WCButton class here
         class WCButton extends HTMLElement {
             //...
         }
         window.customElements.define(‘wc-button', WCButton);
    }
};

WebComponents：Firefox 自定义元素未显示

WebComponents: Firefox custom-element is not showing

javascript

firefox

web-component

custom-element