blocks|key|2617780|text|这是因为当你写下：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2617781|customElements.define('app-list',
++++class+AppList+extends+HTMLElement+{}
);|code-block|syntax|javascript|2617782|类AppList仅在define()调用的作用域中定义。这就是为什么在第二个导入文件中使用它之后看不到它的原因。|offset|length|style|CODE|2617783|相反，您应该首先定义类(全局)，然后在自定义元素定义中使用它：|2617784|//+app-list.html

<script>
++++class+AppList+extends+HTMLElement+{
++++++constructor()+{
++++++++super();
++++++}
++++}++++++++
++++window.customElements.define('app-list',+AppList);
</script>|2617785|entityMap^0|0|0|1|7|A|8|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]|$I|X|J|Y|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|R|$]]

<p>It's because when you write:</p>

<pre><code>customElements.define('app-list',
    class AppList extends HTMLElement {}
);
</code></pre>

<p>the class <code>AppList</code> is defined only in in the scope of the <code>define()</code> call. That's why it's not seen when you use it after in the second import file.</p>

<p>Instead, you should first define the class (globally) and then use it in the custom element definition:</p>

<pre><code>// app-list.html

&lt;script&gt;
    class AppList extends HTMLElement {
      constructor() {
        super();
      }
    }        
    window.customElements.define('app-list', AppList);
&lt;/script&gt;
</code></pre>


blocks|key|94121|text|感谢@Supersharp，我重写了我的自定义组件声明：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|94122|//+app-list.html++++
<script>
++++class+AppList+extends+HTMLElement+{+...+}
++++customElements.define('app-list',+AppList);
</script>|code-block|syntax|javascript|94123|和calcs-list.html|offset|length|style|CODE|94124|<script>
++++class+CalcsList+extends+AppList+{+...+}
++++customElements.define('calcs-list',+CalcsList);
</script>|94125|注意事项:如果在父元素(要扩展的元素)中使用id声明标记，那么这将与扩展元素对super()的调用冲突。|94126|例如：|94127|<template+id="app-list">+
++++...+
</template>|94128|解决此问题的方法是使用the+Google+Developers引用的JavaScript字符串文字，而根本不使用id。|94129|<script>

++++let+template+=+document.createElement('template');
++++template.innerHTML+=+`
++++++++<style>+...+</style>
++++++++<div>+...+</div>
++++`;

++++class+AppList+extends+HTMLElement+{
++++++++constructor()+{
++++++++++++super();
++++++++++++let+shadowRoot+=+this.attachShadow({mode:+'open'}).appendChild(template.content.cloneNode(true));
++++++++}
++++}

</script>|94130|entityMap|0|LINK|mutability|MUTABLE|url|https://developers.google.com/web/fundamentals/web-components/customelements#shadowdom^0|0|0|1|F|0|0|M|2|13|7|0|0|0|1L|2|B|L|0|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|18|8|@$I|19|J|1A|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|1B|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|1C|8|@$I|1D|J|1E|K|L]|$I|1F|J|1G|K|L]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1H|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|1I|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|1J|8|@$I|1K|J|1L|K|L]]|9|@$I|1M|J|1N|1|1O]]|A|$]]|$1|W|3|X|5|D|7|1P|8|@]|9|@]|A|$E|F]]|$1|Y|3|-4|5|6|7|1Q|8|@]|9|@]|A|$]]]|Z|$10|$5|11|12|13|A|$14|15]]]]

<p>Thanks to @Supersharp, I re-wrote my custom component declaration as such:</p>

<pre><code>// app-list.html    
&lt;script&gt;
    class AppList extends HTMLElement { ... }
    customElements.define('app-list', AppList);
&lt;/script&gt;
</code></pre>

<p>And <code>calcs-list.html</code>:</p>

<pre><code>&lt;script&gt;
    class CalcsList extends AppList { ... }
    customElements.define('calcs-list', CalcsList);
&lt;/script&gt;
</code></pre>

<p><em>A note of caution:</em> If you declare a  tag within the parent element (the element that's being extended) with an <code>id</code> then this will conflict with the extended element's call to <code>super()</code>.</p>

<p>For example:</p>

<pre><code>&lt;template id="app-list"&gt; 
    ... 
&lt;/template&gt;
</code></pre>

<p>The way to work around this is to use a JavaScript string literal, as referenced by <a href="https://developers.google.com/web/fundamentals/web-components/customelements#shadowdom" rel="nofollow noreferrer">the Google Developers</a>, and not use an <code>id</code> at all.</p>

<pre><code>&lt;script&gt;

    let template = document.createElement('template');
    template.innerHTML = `
        &lt;style&gt; ... &lt;/style&gt;
        &lt;div&gt; ... &lt;/div&gt;
    `;

    class AppList extends HTMLElement {
        constructor() {
            super();
            let shadowRoot = this.attachShadow({mode: 'open'}).appendChild(template.content.cloneNode(true));
        }
    }

&lt;/script&gt;
</code></pre>


<p>I have a custom Web Component, <code>&lt;app-list&gt;</code> that I'm trying to extend into <code>&lt;calcs-list&gt;</code>.</p>

<pre><code>// app-list.html

&lt;script&gt;
    window.customElements.define('app-list',

        class AppList extends HTMLElement {
            constructor() {
                super();
            }
        }

    );
&lt;/script&gt;
</code></pre>

<p>In calcs-list.html I've got:</p>

<pre><code>&lt;link rel="import" href="app-list.html"&gt;
&lt;script&gt;

window.customElements.define('calcs-list',

    class CalcsList extends AppList {

        constructor() {
            super();
            console.log('CalcsList constructed');
        }

    }

);

&lt;/script&gt;
</code></pre>

<p>However, I get the error </p>

<blockquote>
  <p>Uncaught ReferenceError: AppList is not defined at calcs-list.html:11</p>
</blockquote>

<p>Line 11 references <code>class CalcsList extends AppList {</code></p>

<p>Both files are siblings of the same folder. I tried using an absolute path when importing <code>app-list.html</code> into <code>calcs-list.html</code> but got the same result.</p>

<p>I also tried importing both components into my main index.html file:</p>

<pre><code>//index.html
&lt;link rel="import" href="/src/components/app-list.html"&gt;
&lt;link rel="import" href="/src/components/calcs-list.html"&gt;

&lt;app-list&gt;&lt;/app-list&gt;
&lt;calcs-list&gt;&lt;/calcs-list&gt;
</code></pre>

<p>But experience the same result.</p>

<p>The <code>app-list</code> component works in my application without any issue.</p>

<p>I'm scratching my head on this one and because Web Components are considerably new, there isn't a whole lot of troubleshooting info online, especially with V1 of Web Components.</p>

<p>Thanks!</p>


extend custom element web components v1

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个自定义组件<app-list>，我正试图将其扩展到<calcs-list>中。// app-list.html<script>    window.customElements.define('app-list',        class AppList extends HTMLElement {      ...

问扩展自定义元素web组件v1
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