function truncateText(element, maxLength) {
  const text = element.innerText;
  if (text.length <= maxLength) return;

  const truncatedText = text.slice(0, maxLength);
  const lastSpaceIndex = truncatedText.lastIndexOf(' ');

  element.innerText = truncatedText.slice(0, lastSpaceIndex) + '...';
}

const headlineElement = document.getElementById('headline');
truncateText(headlineElement, 100);

#head {
  width: 300px;
  font-size: 20px;
  display: -webkit-box !important;
  color: #000000 !important;
  -webkit-line-clamp: 4 !important;
  -webkit-box-orient: vertical !important;
  overflow: hidden !important;
}

<div id="head">
  <span id="headline">
            Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a
        </span>
</div>

在此代码中，JavaScript 函数 truncateText 用于在文本内容超过指定的最大长度时截断文本内容。该函数查找最大长度内的最后一个空格字符，并用省略号替换剩余的文本。

在添加省略号之前，您可以将 maxLength 参数调整为所需的字符数。