highlighter.js

const highlightText = (str, match) => {
  if (!str) return null;
  if (!match) return str;
  const regex = new RegExp(match, 'mig');
  return `>${str}<`.replace(/>[^<]+</gmi, (match) => match.replace(regex, '[$]')).slice(1, -1);
};

console.log(highlightText('lorem 0 erty o', 'o'));
console.log(highlightText('<p class="lorem">lorem ipsum dolor sit amet</p>', 'o'));
// l[$]rem 0 erty [$]
// <p class="lorem">l[$]rem ipsum d[$]l[$]r sit amet</p>

// https://jsfiddle.net/aShulz/7dgjn51c/