<template>: 内容模板元素

<table id="producttable">
  <thead>
    <tr>
      <td>UPC_Code</td>
      <td>Product_Name</td>
    </tr>
  </thead>
  <tbody>
    <!-- existing data could optionally be included here -->
  </tbody>
</table>

<template id="productrow">
  <tr>
    <td class="record"></td>
    <td></td>
  </tr>
</template>

// Test to see if the browser supports the HTML template element by checking
// for the presence of the template element's content attribute.
if ("content" in document.createElement("template")) {
  // Instantiate the table with the existing HTML tbody
  // and the row with the template
  const tbody = document.querySelector("tbody");
  const template = document.querySelector("#productrow");

  // Clone the new row and insert it into the table
  const clone = template.content.cloneNode(true);
  let td = clone.querySelectorAll("td");
  td[0].textContent = "1235646565";
  td[1].textContent = "Stuff";

  tbody.appendChild(clone);

  // Clone the new row and insert it into the table
  const clone2 = template.content.cloneNode(true);
  td = clone2.querySelectorAll("td");
  td[0].textContent = "0384928528";
  td[1].textContent = "Acme Kidney Beans 2";

  tbody.appendChild(clone2);
} else {
  // Find another way to add the rows to the table because
  // the HTML template element is not supported.
}

table {
  background: #000;
}
table td {
  background: #fff;
}

<p hidden>
  ⛔ Your browser doesn't support <code>shadowrootmode</code> attribute yet.
</p>
<article>
  <style>
    p {
      padding: 8px;
      background-color: wheat;
    }
  </style>
  <p>I'm in the DOM.</p>
</article>
<article>
  <template shadowrootmode="open">
    <style>
      p {
        padding: 8px;
        background-color: plum;
      }
    </style>
    <p>I'm in the shadow DOM.</p>
  </template>
</article>

const isShadowRootModeSupported =
  HTMLTemplateElement.prototype.hasOwnProperty("shadowRootMode");

document
  .querySelector("p[hidden]")
  .toggleAttribute("hidden", isShadowRootModeSupported);

<div>
  <template shadowrootmode="open">
    <style>
      :host {
        display: block;
        border: 1px dotted black;
        padding: 10px;
        margin: 10px;
      }
      :focus {
        outline: 2px solid blue;
      }
    </style>
    <div>Clickable Shadow DOM text</div>
    <input type="text" placeholder="Input inside Shadow DOM" />
  </template>
</div>

<div>
  <template shadowrootmode="open" shadowrootdelegatesfocus>
    <style>
      :host {
        display: block;
        border: 1px dotted black;
        padding: 10px;
        margin: 10px;
      }
      :focus {
        outline: 2px solid blue;
      }
    </style>
    <div>Clickable Shadow DOM text</div>
    <input type="text" placeholder="Input inside Shadow DOM" />
  </template>
</div>

div:focus {
  border: 2px solid red;
}

<div id="container"></div>

<template id="template">
  <div>Click me</div>
</template>

const container = document.getElementById("container");
const template = document.getElementById("template");

function clickHandler(event) {
  event.target.append(" — Clicked this div");
}

const firstClone = template.content.cloneNode(true);
firstClone.addEventListener("click", clickHandler);
container.appendChild(firstClone);

const secondClone = template.content.cloneNode(true);
secondClone.children[0].addEventListener("click", clickHandler);
container.appendChild(secondClone);