WebComponent使用教程-爱站

WebComponent 是官方定义的自定义组件实现方式，它可以让开发者不依赖任何第三方框架（如Vue，React）来实现自定义页面组件；达到组件复用效果

一个简单例子，让页面显示 hello world：

<body>
  <!-- 使用组件的方式 -->
  <my-text />
  <script>
    class MyText extends HTMLElement {
      constructor() {
        super();
        this.append("hello world");
      }
    }
    window.customElements.define("my-text", MyText);
  </script>
</body>

三项主要技术

1、Custom elements （自定义元素）

一组 JavaScript API，允许您定义 custom elements 及其行为，然后可以在您的用户界面中按照需要使用它们

分为两种形式：

自主定制元素：是独立的元素，它不继承其他内建的 HTML 元素，可以直接把它们写成 HTML 标签的形式，来在页面上使用，例如我们刚才自定义的 <my-text>

自定义内置元素：继承自内置的 HTML 元素。指定所需扩展的元素

使用时需通过 is 属性指定 custom element 的名称，必须包含一个短横线
注册的时候必须使用 extends 的属性

<!-- 自定义内置元素 使用 is-->
<body>
  <!-- 使用组件的方式 -->
  <p is="color-p" color="green">云牧</p>
  <script>
    class ColorP extends HTMLParagraphElement {
      constructor() {
        super();
        this.style.color = this.getAttribute("color");
      }
    }
    window.customElements.define("color-p", ColorP, { extends: "p" });
  </script>
</body>

推荐在 connectedCallback 生命周期函数，处理节点操作

<!-- 自主定制元素-->
<body>
  <my-text />
  <script>
    class MyText extends HTMLElement {
      constructor() {
        super();
      }
      connectedCallback() {
        this.append("hello world");
      }
    }
    window.customElements.define("my-text", MyText);
  </script>
</body>

生命周期函数

connectedCallback：插入文档时，可能被多次触发，比如删除后又添加到文档

disconnectedCallback：从文档删除时，可配置做清理工作

adoptedCallback：被移动新文档时

attributeChangedCallback：属性变化时

配合 observedAttributess 属性一起使用，指定监听的属性
使用 setAttribute 方法更新属性

不同操作触发的生命周期函数：

例子：

<body>
  <div id="container">
    <p is="my-text" text="云牧" id="myText"></p>
  </div>
  <button id="btnUpdateText">更新属性</button>
  <button id="btnRemove">删除节点</button>
  <button id="btnRestore">恢复节点</button>
  <button id="btnAdopt">移动节点</button>
  <iframe src="./ifr.html" id="ifr"></iframe>
  <script>
    class MyText extends HTMLParagraphElement {
      constructor() {
        super();
      }
      connectedCallback() {
        console.log("生命周期:connectedCallback");
        this.append("你好:" + this.getAttribute("text"));
      }
      disconnectedCallback() {
        console.log("生命周期:disconnectedCallback");
        this.innerHTML = "";
      }
      // 监测的属性
      static get observedAttributes() {
        return ["text"];
      }
      attributeChangedCallback(name, oldValue, newValue) {
        console.log("生命周期:attributeChangedCallback", name, oldValue, newValue);
        // 最先触发是此函数，判断是不是第一次触发，第一次的话，只由 connectedCallback 处理
        if (oldValue != null) {
          this.replaceChildren("你好:" + newValue);
        }
      }
      adoptedCallback() {
        console.log("生命周期:adoptedCallback");
      }
    }
    window.customElements.define("my-text", MyText, { extends: "p" });
    const myText = document.getElementById("myText");
    btnUpdateText.addEventListener("click", function (e) {
      myText.setAttribute("text", "黛玉");
    });
    btnRemove.addEventListener("click", function (e) {
      myText.remove();
    });
    btnRestore.addEventListener("click", function (e) {
      container.appendChild(myText);
    });
    btnAdopt.addEventListener("click", () => {
      const textNode = ifr.contentWindow.document.getElementById("myText");
      container.appendChild(document.adoptNode(textNode));
    });
  </script>
</body>

2、HTML templates（HTML 模板）

使用 JS 模板字串符的方式创建模板，提示不友好，复用性差

<body>
  <product-item
    name="关东煮"
    img="//img10.360buyimg.com/seckillcms/s200x200_jfs/t1/121953/18/20515/175357/61e7dc79Ee0acbf20/4f4f56abd2ea2f75.jpg!cc_200x200.webp"
    price="49.8"
  ></product-item>
  <script>
    class ProductItem extends HTMLElement {
      constructor() {
        super();
      }
      connectedCallback() {
        const content = `
                  <img class="img" src="https://misc.360buyimg.com/lib/skin/e/i/error-jd.gif" />
                  <div class="name"></div>
                  <div class="price"></div>
              `;
        this.innerHTML = content;
        this.querySelector(".img").src = this.getAttribute("img");
        this.querySelector(".name").innerText = this.getAttribute("name");
        this.querySelector(".price").innerText = this.getAttribute("price");
      }
    }
    window.customElements.define("product-item", ProductItem);
  </script>
</body>

template 方式

<body>
  <!-- template -->
  <template id="tpl-product-item">
    <img class="img" src="https://misc.360buyimg.com/lib/skin/e/i/error-jd.gif" />
    <div class="name"></div>
    <div class="price"></div>
  </template>
  <product-item
    name="关东煮"
    img="//img10.360buyimg.com/seckillcms/s200x200_jfs/t1/121953/18/20515/175357/61e7dc79Ee0acbf20/4f4f56abd2ea2f75.jpg!cc_200x200.webp"
    price="49.8"
  ></product-item>
  <script>
    class ProductItem extends HTMLElement {
      constructor() {
        super();
      }
      connectedCallback() {
        const content = document.getElementById("tpl-product-item").content.cloneNode(true);
        // 插入克隆的模板内容
        this.append(content);
        this.querySelector(".img").src = this.getAttribute("img");
        this.querySelector(".name").innerText = this.getAttribute("name");
        this.querySelector(".price").innerText = this.getAttribute("price");
      }
    }
    window.customElements.define("product-item", ProductItem);
  </script>
</body>

slot

<body>
  <template id="tpl-test">
    <style>
      .title {
        color: green;
      }
    </style>
    <div class="title">标题</div>
    <slot name="slot-des">默认内容</slot>
  </template>
  <test-item>
    <div slot="slot-des">不是默认内容</div>
  </test-item>
  <script>
    class TestItem extends HTMLElement {
      constructor() {
        super();
      }
      connectedCallback() {
        const content = document.getElementById("tpl-test").content.cloneNode(true);
        const shadow = this.attachShadow({ mode: "open" });
        shadow.append(content);
      }
    }
    window.customElements.define("test-item", TestItem);
  </script>
</body>

3、Shadow DOM（影子 DOM）

影子DOM，其内部样式不共享

<body>
  <!--  不受外部 .container.container 的颜色影响 -->
  <my-item-s></my-item-s>
  <div class="container">My item</div>
  <style>
    .container.container {
      color: green;
    }
  </style>
  <template id="tpl">
    <style>
      .container {
        color: pink;
      }
    </style>
    <div class="container">My Item</div>
  </template>
  <script>
    class MyItemShadow extends HTMLElement {
      constructor() {
        super();
      }
      connectedCallback() {
        const content = document.getElementById("tpl").content.cloneNode(true);
        const shadow = this.attachShadow({ mode: "open" });
        shadow.append(content);
      }
    }
    window.customElements.define("my-item-s", MyItemShadow);
  </script>
</body>

影子DOM，其内部元素不可以直接被访问到

有一个重要的参数 mode

open： shadow root 元素通过 js 从外部访问根节点
closed：拒绝 js 从外部访问关闭的 shadow root 节点

<body>
  <template id="tpl">
    <div class="title"></div>
    <div class="des"></div>
  </template>
  <note-item class="note-item" title="标题" des="内容"></note-item>
  <script>
    class NoteItem extends HTMLElement {
      constructor() {
        super();
      }
      connectedCallback() {
        const content = document.getElementById("tpl").content.cloneNode(true);
        const shadow = this.attachShadow({ mode: "open" });
        shadow.append(content);
        // 如果是 open 则可以继续访问操作内部 dom
        // console.log(document.querySelector(".note-item").shadowRoot.querySelector(".title"));
        shadow.querySelector(".title").textContent = this.getAttribute("title");
        shadow.querySelector(".des").textContent = this.getAttribute("des");
      }
    }
    window.customElements.define("note-item", NoteItem);
  </script>
</body>

引入外部样式：

<body>
  <template id="tpl">
    <!-- 方式一: -->
    <link rel="stylesheet" href="index.css" rel="external nofollow"  />
    <div>My Item</div>
  </template>
  <my-item></my-item>
  <script>
    class MyItem extends HTMLElement {
      constructor() {
        super();
      }
      connectedCallback() {
        const content = document.getElementById("tpl").content.cloneNode(true);
        const shadow = this.attachShadow({ mode: "open" });
        shadow.append(content);
        // 方式二:
        const linkEl = document.createElement("link");
        linkEl.setAttribute("rel", "stylesheet");
        linkEl.setAttribute("href", "index.css");
        shadow.appendChild(linkEl);
      }
    }
    window.customElements.define("my-item", MyItem);
  </script>
</body>

动态创建 webComponent 组件例子

通过创建商品组件，并使得点击能跳转

<body>
  <div id="product-list" style="display: flex"></div>
  <template id="product-item">
    <style>
      .product-item {
        margin-left: 15px;
        cursor: pointer;
      }
      .img {
        width: 100px;
      }
      .name {
        text-align: center;
      }
      .price {
        color: #999;
        text-align: center;
      }
    </style>
    <div class="product-item">
      <img class="img" src="https://misc.360buyimg.com/lib/skin/e/i/error-jd.gif" />
      <div class="name"></div>
      <div class="price"></div>
    </div>
  </template>
  <script>
    class ProductItemElement extends HTMLElement {
      constructor(props) {
        super(props);
        this.addEventListener("click", () => {
          window.open(`https://item.jd.com/${this.id}.html`);
        });
      }
      connectedCallback() {
        const shadow = this.attachShadow({ mode: "open" });
        const content = document.getElementById("product-item").content.cloneNode(true);
        content.querySelector(".img").src = this.img;
        content.querySelector(".name").innerText = this.name;
        content.querySelector(".price").innerText = this.price;
        shadow.appendChild(content);
      }
    }
    window.customElements.define("product-item", ProductItemElement);
  </script>
  <script>
    const products = [
      {
        name: "关东煮",
        img: "//img10.360buyimg.com/seckillcms/s200x200_jfs/t1/121953/18/20515/175357/61e7dc79Ee0acbf20/4f4f56abd2ea2f75.jpg!cc_200x200.webp",
        id: "10026249568453",
        price: 49.8
      },
      {
        name: "土鸡蛋",
        img: "//img11.360buyimg.com/seckillcms/s200x200_jfs/t1/172777/32/27438/130981/61fbd2e0E236000e0/7f5284367e2f5da6.jpg!cc_200x200.webp",
        id: "10024773802639",
        price: 49.8
      },
      {
        name: "东北蜜枣粽子",
        img: "//img20.360buyimg.com/seckillcms/s200x200_jfs/t1/129546/31/19459/110768/60b1f4b4Efd47366c/3a5b80c5193bc6ce.jpg!cc_200x200.webp",
        id: "10035808728318",
        price: 15
      }
    ];
    const productList = document.getElementById("product-list");
    const elList = products.map(product => {
      // 创建组件
      const el = document.createElement("product-item");
      el.img = product.img;
      el.name = product.name;
      el.price = product.price;
      el.id = product.id;
      return el;
    });
    productList.append.apply(productList, elList);
  </script>
</body>