JSFiddle - React, Tailwind, and code Playground

HTML

<textarea id="input">&lt;p&gt;hoge&lt;br /&gt;
foo&lt;br /&gt;
piyo&lt;/p&gt;
&lt;pre&gt;
&lt;code&gt;hoge&lt;/code&gt; &lt;code&gt;
foo&lt;span&gt;hoge
&lt;/span&gt;
&lt;/code&gt;
&lt;/pre&gt;
&lt;p&gt;hoge&lt;/p&gt;</textarea>

<input type="button" value="delete CR&amp;LF" onclick="deleteCRLF();">

<textarea id="output"></textarea>

<ul>
  <li><a href="http://hibari.2ch.net/test/read.cgi/hp/1296794731/953n-">Webサイト制作初心者用質問スレ part223</a></li>
</ul>

CSS

textarea { display: block; width: 80%; height: 11em; }

JavaScript

function deleteCRLF() {
  document.getElementById('output').value = document.getElementById('input').value.replace(/\u003Cpre\u003E[\s\S]*?\u003C\u002Fpre\u003E|\r\n|[\n\r]/gi, function (token) {
    switch (token) {
      case '\r\n':
      case '\r':
      case '\n':
        token = '';
        break;
    }

    return token;
  });
}