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+---
+title: CustomElementRegistry.define()
+slug: Web/API/CustomElementRegistry/define
+tags:
+  - API
+  - CustomElementRegistry
+  - Web Components
+  - custom elements
+translation_of: Web/API/CustomElementRegistry/define
+---
+<p>{{APIRef("CustomElementRegistry")}}</p>
+
+<p>{{domxref("CustomElementRegistry")}}接口的<code><strong>define()</strong></code>方法定义了一个自定义元素。</p>
+
+<p>你可以创建两种类型的自定义元素：</p>
+
+<ul>
+ <li><strong>自主定制元素</strong>：独立元素; 它们不会从内置HTML元素继承。</li>
+ <li><strong>自定义内置元素</strong>：这些元素继承自 - 并扩展 - 内置HTML元素</li>
+</ul>
+
+<h2 id="语法">语法</h2>
+
+<pre class="syntaxbox">customElements.define(<em>name</em>, <em>constructor</em>, <em>options</em>);
+</pre>
+
+<h3 id="参数">参数</h3>
+
+<dl>
+ <dt>name</dt>
+ <dd>自定义元素名.</dd>
+ <dt>constructor</dt>
+ <dd>自定义元素构造器.</dd>
+ <dt>options {{optional_inline}}</dt>
+ <dd>控制元素如何定义. 目前有一个选项支持:
+ <ul>
+  <li><code>extends</code>. 指定继承的已创建的元素. 被用于创建自定义元素.</li>
+ </ul>
+ </dd>
+</dl>
+
+<h3 id="返回值">返回值</h3>
+
+<p>空</p>
+
+<h2 id="示例">示例</h2>
+
+<h3 id="自主定制元素">自主定制元素</h3>
+
+<p>以下代码取自我们的 <a href="https://github.com/mdn/web-components-examples/tree/master/popup-info-box-web-component">popup-info-box-web-component</a> 示例(<a href="https://mdn.github.io/web-components-examples/popup-info-box-web-component/">see it live also</a>)。</p>
+
+<pre class="brush: js">// Create a class for the element
+class PopUpInfo extends HTMLElement {
+  constructor() {
+    // Always call super first in constructor
+    super();
+
+    // Create a shadow root
+    var shadow = this.attachShadow({mode: 'open'});
+
+    // Create spans
+    var wrapper = document.createElement('span');
+    wrapper.setAttribute('class','wrapper');
+    var icon = document.createElement('span');
+    icon.setAttribute('class','icon');
+    icon.setAttribute('tabindex', 0);
+    var info = document.createElement('span');
+    info.setAttribute('class','info');
+
+    // Take attribute content and put it inside the info span
+    var text = this.getAttribute('text');
+    info.textContent = text;
+
+    // Insert icon
+    var imgUrl;
+    if(this.hasAttribute('img')) {
+      imgUrl = this.getAttribute('img');
+    } else {
+      imgUrl = 'img/default.png';
+    }
+    var img = document.createElement('img');
+    img.src = imgUrl;
+    icon.appendChild(img);
+
+    // Create some CSS to apply to the shadow dom
+    var style = document.createElement('style');
+
+    style.textContent = '.wrapper {' +
+                           'position: relative;' +
+                        '}' +
+
+                         '.info {' +
+                            'font-size: 0.8rem;' +
+                            'width: 200px;' +
+                            'display: inline-block;' +
+                            'border: 1px solid black;' +
+                            'padding: 10px;' +
+                            'background: white;' +
+                            'border-radius: 10px;' +
+                            'opacity: 0;' +
+                            'transition: 0.6s all;' +
+                            'position: absolute;' +
+                            'bottom: 20px;' +
+                            'left: 10px;' +
+                            'z-index: 3;' +
+                          '}' +
+
+                          'img {' +
+                            'width: 1.2rem' +
+                          '}' +
+
+                          '.icon:hover + .info, .icon:focus + .info {' +
+                            'opacity: 1;' +
+                          '}';
+
+    // attach the created elements to the shadow dom
+
+    shadow.appendChild(style);
+    shadow.appendChild(wrapper);
+    wrapper.appendChild(icon);
+    wrapper.appendChild(info);
+  }
+}
+
+// Define the new element
+customElements.define('popup-info', PopUpInfo);</pre>
+
+<pre><code>&lt;popup-info img="img/alt.png" text="Your card validation code (CVC) is an extra
+                                    security feature — it is the last 3 or 4
+                                    numbers on the back of your card."&gt;</code></pre>
+
+<div class="note">
+<p><strong>注意</strong>：自主自定义元素的构造函数必须扩展{{domxref("HTMLElement")}}。</p>
+</div>
+
+<h3 id="自定义内置元素">自定义内置元素</h3>
+
+<p>以下代码取自我们的 <a href="https://github.com/mdn/web-components-examples/tree/master/word-count-web-component">word-count-web-component</a> 实例 (<a href="https://mdn.github.io/web-components-examples/word-count-web-component/">查看实例效果</a>).</p>
+
+<pre class="brush: js">// 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' });</pre>
+
+<pre class="brush: html"><code>&lt;p is="word-count"&gt;&lt;/p&gt;</code>
+</pre>
+
+<h2 id="规范">规范</h2>
+
+<table class="standard-table">
+ <tbody>
+  <tr>
+   <th scope="col">Specification</th>
+   <th scope="col">Status</th>
+   <th scope="col">Comment</th>
+  </tr>
+  <tr>
+   <td>{{SpecName("HTML WHATWG", "custom-elements.html#dom-customelementregistry-define", "customElements.define()")}}</td>
+   <td>{{Spec2("HTML WHATWG")}}</td>
+   <td>Initial definition.</td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="浏览器兼容">浏览器兼容</h2>
+
+<div class="hidden">
+<p>The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p>
+</div>
+
+<p>{{Compat("api.CustomElementRegistry.define")}}</p>