这是我在要求一个（更短的）正则表达式解决方案之前的尝试：

const dFrag = document.createDocumentFragment();
str.textContent.split('<br>').forEach(substr => {
  const div = document.createElement('div');
  let ul;
  if (!substr) {
    substr = '<br>';
  }
  div.innerHTML = substr;
  ul = div.querySelector('ul');
  if (ul) {
    dFrag.appendChild(ul);
  } else {
    dFrag.appendChild(div);
  }
});
str.innerHTML = '';
str.appendChild(dFrag);

"You can't parse [HTML] with regex. [...] Have you tried using an [HT]ML parser instead?" ™
（更简洁的版本可以在下面的片段中找到）

function replaceTextBrWithDiv(html) {
  // Create an element that acts as a parser
  const parser = document.createElement('div');
  parser.innerHTML = html;

  // Modify an array-like when iterating over it may cause some issues.
  // Copy it first.
  const childNodes = [...parser.childNodes];

  // Index-based iterating
  for (let index = 0; index < childNodes.length; index++) {
    const node = childNodes[index];
    const nextNode = childNodes[index + 1];

    if (node instanceof Text && nextNode instanceof HTMLBRElement) {
      const div = document.createElement('div');

      // Remove text node from parser and append it to div
      div.appendChild(node);
      nextNode.replaceWith(div);

      // Skip next node (i.e. <br>)
      index++;
    }
  }

  return parser.innerHTML;
}

试试看：

console.config({ maximize: true });

function replaceTextBrWithDiv(html) {
  const parser = document.createElement('div');
  parser.innerHTML = html;

  parser.childNodes.forEach((node, index, nodes) => {
    const nextNode = nodes[index + 1];
    
    if (node instanceof Text && nextNode instanceof HTMLBRElement) {
      const div = document.createElement('div');
      div.appendChild(node);
      nextNode.replaceWith(div);
    }
  });
  
  return parser.innerHTML;
}

const content = 'text<br>text<br><ul><li>text</li></ul><br>';

console.log(replaceTextBrWithDiv(content));

<script src="https://gh-canon.github.io/stack-snippet-console/console.min.js"></script>

如果你更喜欢使用正则表达式，可以使用 /（？！<li.？>）（？！）（？！<ul.？>）（？！）（.？）
/g*

const html = 'text<br>text<br><ul><li>text</li></ul><br>';
const regex = /(?!<li.*?>)(?!<\/li>)(?!<ul.*?>)(?!<\/ul>)(.*?)<br>/g;
const replacedHtml = html.replace(regex, '<div>$1</div>');
console.log(replacedHtml);

但是如果您切换到HTML解析器来轻松地导航和修改HTML内容的结构，那就更好了