> For the complete documentation index, see [llms.txt](https://lochiwei.gitbook.io/web/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://lochiwei.gitbook.io/web/component/template/slot/slotted-elements.md).

# slotted nodes

[web](/web/master.md) ⟩ [component](/web/component.md) ⟩ [slot](/web/component/template/slot.md) ⟩ slotted nodes

{% hint style="info" %}
任何在自訂 [web component](/web/component.md) 標籤(如：<mark style="color:blue;">`<my-component>`</mark>)之間的<mark style="color:yellow;">直接子元素</mark>(direct child)，包含文字(text node)，都是 *<mark style="color:purple;">**slotted nodes**</mark>*，例如：

```html
<my-component>
  <!-- ⭐️ slotted nodes -->
  <!-- ⭐️ 沒有指定 slot -->
  <p>This is a slotted node.</p>
  <!-- ⭐️ 指定 slot="username" -->
  <div slot="username"><span>John Smith</span></div>
</my-component>
```

{% endhint %}

{% tabs %}
{% tab title="👥 相關" %}

* [\<slot>](/web/component/template/slot.md)
* [named slot](/web/component/template/slot/named-slot.md)
* [Styling in Shadow DOM](/web/component/shadow-dom/styles.md#cheat-sheet) ⟩ **::slotted()**
* [**Use CSS Variables**](/web/component/shadow-dom/styles/css-vars.md)
  {% endtab %}

{% tab title="📗 參考" %}

* 📗 JS.info ⟩ [Styling slotted content](https://javascript.info/shadow-dom-style#styling-slotted-content)
* 👉 [Styling in Shadow DOM](/web/component/shadow-dom/styles.md#cheat-sheet) - :host, :host(), :host-context(), ::slotted()
  {% endtab %}

{% tab title="📘 手冊" %}

* MDN ⟩ [Using templates and slots](https://developer.mozilla.org/en-US/docs/Web/Web_Components/Using_templates_and_slots)
  {% endtab %}
  {% endtabs %}

{% hint style="info" %}

* Nodes (in **light DOM**) that can be **inserted** into **\<slot>** are known as ***slottable*****&#x20;nodes**; when a node **has been inserted** in a \<slot>, it is said to be ***slotted***.<br>
* An **unnamed** [`<slot>`](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/slot) will be **filled with** all of the **custom element'**&#x73; **top-level child nodes** that **do not have** the [`slot`](https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes#attr-slot) attribute. This **includes text nodes**.\
  📘 [Using templates and slots](https://developer.mozilla.org/en-US/docs/Web/Web_Components/Using_templates_and_slots#adding_flexibility_with_slots)
  {% endhint %}

{% hint style="danger" %}

* Only **custom element**'s **top-level children** (in the **light DOM**) may have **`[slot]`** attribute❗️ 👉 See "**light DOM**" tab in example code in [Using Slots](/web/component/shadow-dom/slots.md#code-example).
* **::slotted()** only select **slotted element** itself, **not its descendants** (content)❗️
  {% endhint %}

## Slotted Contents

{% hint style="warning" %}

* **slotted content** come from **light DOM**, they use **document styles**❗️
* **shadow DOM** styles **do not** affect **slotted content**❗️
* **::slotted()** only select **slotted element** itself, **not** its **descendants (content)**❗️
* **::slotted()** **can't go inside light DOM**, for example:  **::slotted(div) p** is **invalid**❗️
* **::slotted()** can't be used in **.querySelector()**❗️
  {% endhint %}

👉 [Styling in Shadow DOM](/web/component/shadow-dom/styles.md#pseudo-class)

在下面的範例碼中，我們分別在**外部**及**內部 CSS** 對 **`<span>`** 元素做「**粗體**」與「**紅色**」格式設定，對於插入 **shadow DOM`<slot>`** 的 **`<span>`** 而言，只有**外部**的「**粗體**」設定有效 (👉 see: "**codepen**" tab below)。 💾 [replit](https://replit.com/@pegasusroe/slotted#index.html)

{% tabs %}
{% tab title="html" %}

```markup
<!-- ⭐️ document (outer) styles -->
<style>
  span {
    font-weight: bold
  }
</style>

<!-- ⭐️ custom element -->
<user-card>
  <!-- ⭐️ slotted element -->
  <div slot="username">
    <!--  
      ⭐️ slotted content is affected by document (outer) styles,
         not by local (shadow DOM) styles❗️  
    -->
    <span>John Smith</span>
  </div>
</user-card>

<script>
  customElements.define('user-card', class extends HTMLElement {
    connectedCallback() {
      this.attachShadow({mode: 'open'});
      
      // ⭐️ shadow tree (with named <slot>)
      // 1. slotted elements come from light DOM, they use document styles. 
      // 2. local styles do not affect slotted content.
      this.shadowRoot.innerHTML = `
        <style>
          span { background: red; }
        </style>
        Name: <slot name="username"></slot>
      `;
    }
  });
</script>
```

{% endtab %}

{% tab title="codepen" %}
{% embed url="<https://codepen.io/lochiwei/pen/LYLeRWZ>" %}

{% endtab %}
{% endtabs %}

### Styling Slotted Content

💾 [::slotted() lab](https://replit.com/@pegasusroe/slotted-lab#index.html)

* use document (**outer**) styles (in **light DOM**).
* style **\<slot>**  (in **shadow DOM**) and rely on **CSS inheritance**.
* use **::slotted(«selector»)** in **shadow DOM**.

{% hint style="info" %}

* ⭐️ use **CSS variables**: \
  CSS variables exist **on all levels**, **both in light and shadow**.\
  👉 [CSS hooks with custom properties](https://javascript.info/shadow-dom-style#css-hooks-with-custom-properties)
  {% endhint %}

{% tabs %}
{% tab title="codepen" %}
{% embed url="<https://codepen.io/lochiwei/pen/mdwpRgO>" %}

{% endtab %}

{% tab title="::slotted() lab" %}

```markup
<!-- ⭐️ document (outer) styles -->
<style>
  span {
    font-weight: bold
  }

  /* ⭐️ select <span> in slotted <p> element */
  p[slot] span {
    background: hsl(90, 90%, 80%);    /* light green */
    padding: 0 8px;
  }
</style>

<!-- ⭐️ custom element -->
<user-card>
  <!-- ⭐️ slotted element -->
  <div slot="username">
    <!--  
       ⭐️ slotted content is affected by document (outer) styles,
          not by local (shadow DOM) styles❗️  
    -->
    <span>John Smith</span>
  </div>
</user-card>

<user-card>
  <span slot="username">Jane Smith</span>
</user-card>

<user-card>
  <p slot="username">
    <span>Doctor Who</span>
  </p>
</user-card>

<script>
  customElements.define('user-card', class extends HTMLElement {
    connectedCallback() {
      this.attachShadow({mode: 'open'});
      
      // ⭐️ shadow tree (with named <slot>)
      // 1. slotted elements come from light DOM, they use document styles. 
      // 2. local styles do not affect slotted content.
      // 3. ::slotted() only select slotted element itself, not its descendants❗️
      this.shadowRoot.innerHTML = `
                <style>
                    :host {
                        border: 1px solid black;
                        margin: 4px;
                        padding: 4px;
                        display: inline-block;
                        box-shadow: 
                            0 4px 8px 0 rgba(0, 0, 0, 0.4), 
                            0 6px 20px 0 rgba(0, 0, 0, 0.19);
                    }
                    :host(:hover) {
                        box-shadow: 
                            0 2px 4px 0 rgba(0, 0, 0, 0.6), 
                            0 3px 10px 0 rgba(0, 0, 0, 0.35);
                    }
                    ::slotted(*) {
                        border: 1px solid black;
                    }
                    ::slotted(span) { 
                        background: pink;
                        padding: 0 6px;
                    }
                    ::slotted(div) {
                        padding: 0 6px;
                        background: hsl(225, 80%, 90%);
                    }
                </style>
                Name: <slot name="username"></slot>
            `;
    }
  });
</script>
```

{% endtab %}

{% tab title="css var demo" %}

```markup
<style>
  /* ⭐️ 2. set css var with custom value */
  user-card {
    --user-card-field-color: green;
  }
</style>

<template id="tmpl">
  <style>
    /* ⭐️ 1. use css var with default value */
    .field {
      color: var(--user-card-field-color, black);
    }
  </style>
  <div class="field">Name: <slot name="username"></slot></div>
  <div class="field">Birthday: <slot name="birthday"></slot></div>
</template>
```

{% endtab %}
{% endtabs %}


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