const regex = /.*(https:\/\/cloud\.saikoanimes\.net\/.*)" c.*/gm;
// Alternative syntax using RegExp constructor
// const regex = new RegExp('.*(https:\\\/\\\/cloud\\.saikoanimes\\.net\\\/.*)" c.*', 'gm')
const str = `
<a href="https://cloud.saikoanimes.net/11Yu" class="btn-sa" target="blank">01</a>
<a href="https://cloud.saikoanimes.net/BXz" class="btn-sa" target="blank">02</a>
<a href="https://cloud.saikoanimes.net/BXv" class="btn-sa" target="blank">03</a>
<a href="https://cloud.saikoanimes.net/11Yx" class="btn-sa" target="blank">04</a>
<a href="https://cloud.saikoanimes.net/BXt" class="btn-sa" target="blank">05</a>
<a href="https://cloud.saikoanimes.net/BXw" class="btn-sa" target="blank">06</a>
<a href="https://cloud.saikoanimes.net/11Yv" class="btn-sa" target="blank">07</a>
<a href="https://cloud.saikoanimes.net/BXx" class="btn-sa" target="blank">08</a>
<a href="https://cloud.saikoanimes.net/BXy" class="btn-sa" target="blank">09</a>
<a href="https://cloud.saikoanimes.net/11Yo" class="btn-sa" target="blank">10</a>
<a href="https://cloud.saikoanimes.net/11Ym" class="btn-sa" target="blank">11</a>
<a href="https://cloud.saikoanimes.net/11Yw" class="btn-sa final" target="blank">12</a> `;
const subst = `$1`;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions