docsify/src/core/render/emojify.js

import { inBrowser } from '../util/env';

function replace(m, $1) {
  return (
    '<img class="emoji" src="https://github.githubassets.com/images/icons/emoji/' +
    $1 +
    '.png" alt="' +
    $1 +
    '" />'
  );
}

export function emojify(text) {
  return text
    .replace(/<(pre|template|code)[^>]*?>[\s\S]+?<\/(pre|template|code)>/g, m =>
      m.replace(/:/g, '__colon__')
    )
    .replace(/:(\w+?):/gi, (inBrowser && window.emojify) || replace)
    .replace(/__colon__/g, ':');
}