CustomElementRegistry

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.

* Some parts of this feature may have varying levels of support.

**CustomElementRegistry**接口提供注册自定义元素和查询已注册元素的方法。要获取它的实例，请使用 window.customElements属性。

方法

CustomElementRegistry.define(): 定义一个新的自定义元素。
CustomElementRegistry.get(): 返回指定自定义元素的构造函数，如果未定义自定义元素，则返回undefined。
CustomElementRegistry.upgrade(): Upgrades a custom element directly, even before it is connected to its shadow root.
CustomElementRegistry.whenDefined(): 返回当使用给定名称定义自定义元素时将会执行的 promise。（如果已经定义了这样一个自定义元素，那么立即执行返回的 promise。）

示例

以下代码来自我们的 word-count-web-component 示例（查看实时运行版本）。请注意我们如何使用 CustomElementRegistry.define() 方法在创建其类后定义自定义元素。

// Create a class for the element
class WordCount extends HTMLParagraphElement {
  constructor() {
    // Always call super first in constructor
    super();

    // count words in element's parent element
    var wcParent = this.parentNode;

    function countWords(node) {
      var text = node.innerText || node.textContent;
      return text.split(/\s+/g).length;
    }

    var count = "Words: " + countWords(wcParent);

    // Create a shadow root
    var shadow = this.attachShadow({ mode: "open" });

    // Create text node and add word count to it
    var text = document.createElement("span");
    text.textContent = count;

    // Append it to the shadow root
    shadow.appendChild(text);

    // Update count when element content changes
    setInterval(function () {
      var count = "Words: " + countWords(wcParent);
      text.textContent = count;
    }, 200);
  }
}

// Define the new element
customElements.define("word-count", WordCount, { extends: "p" });

规范

Specification
HTML # custom-elements-api

浏览器兼容性

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