不确定，但这似乎工作。它非常类似于你的，只需要转义那里的\时，使用new RegExp('', '')语法。

var html = `
  <th>hi 13 hello</th>
  <td>good hello 12</td>
`;

var word = "hello"
var reg = new RegExp('<(?!th)\\b.*>[^<]*(' + word + ')', "ig");
console.log(reg)

var matches = reg.exec(html)
console.log(matches)

这里不需要正则表达式，只要选择<td>元素，并将它们的innerText与query字符串匹配即可。

const results = document.querySelector('#results');

const doesMatch = (text, query) =>
  query.length > 0 && text.toLowerCase().includes(query);

const highlight = (td, query) => {
  td.classList.toggle('highlight', doesMatch(td.innerText, query));
};

const handleSearch = (e) => {
  const query = e.target.value.trim().toLowerCase();
  results.querySelectorAll('td').forEach(td => highlight(td, query));
};

document.querySelector('#query').addEventListener('input', handleSearch);

.highlight { background: yellow; }

<label>Search</label>
<input id="query" type="search" placeholder="Search for a word..." autocomplete="off"/>
<hr />
<table id="results">
  <thead>
    <tr>
      <th colspan="2">List of States</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Alabama</td>
      <td>Montana</td>
    </tr>
    <tr>
      <td>Alaska</td>
      <td>Nebraska</td>
    </tr>
    <tr>
      <td>Arizona</td>
      <td>Nevada</td>
    </tr>
    <tr>
      <td>Arkansas</td>
      <td>New Hampshire</td>
    </tr>
    <tr>
      <td>California</td>
      <td>New Jersey</td>
    </tr>
    <tr>
      <td>Colorado</td>
      <td>New Mexico</td>
    </tr>
    <tr>
      <td>Connecticut</td>
      <td>New York</td>
    </tr>
    <tr>
      <td>Delaware</td>
      <td>North Carolina</td>
    </tr>
    <tr>
      <td>Florida</td>
      <td>North Dakota</td>
    </tr>
    <tr>
      <td>Georgia</td>
      <td>Ohio</td>
    </tr>
    <tr>
      <td>Hawaii</td>
      <td>Oklahoma</td>
    </tr>
    <tr>
      <td>Idaho</td>
      <td>Oregon</td>
    </tr>
    <tr>
      <td>Illinois</td>
      <td>Pennsylvania</td>
    </tr>
    <tr>
      <td>Indiana</td>
      <td>Rhode Island</td>
    </tr>
    <tr>
      <td>Iowa</td>
      <td>South Carolina</td>
    </tr>
    <tr>
      <td>Kansas</td>
      <td>South Dakota</td>
    </tr>
    <tr>
      <td>Kentucky</td>
      <td>Tennessee</td>
    </tr>
    <tr>
      <td>Louisiana</td>
      <td>Texas</td>
    </tr>
    <tr>
      <td>Maine</td>
      <td>Utah</td>
    </tr>
    <tr>
      <td>Maryland</td>
      <td>Vermont</td>
    </tr>
    <tr>
      <td>Massachusetts</td>
      <td>Virginia</td>
    </tr>
    <tr>
      <td>Michigan</td>
      <td>Washington</td>
    </tr>
    <tr>
      <td>Minnesota</td>
      <td>West Virginia</td>
    </tr>
    <tr>
      <td>Mississippi</td>
      <td>Wisconsin</td>
    </tr>
    <tr>
      <td>Missouri</td>
      <td>Wyoming</td>
    </tr>
  </tbody>
</table>