vant/packages/vant-markdown-loader/src/highlight.js

const hljs = require('highlight.js');

module.exports = function highlight(str, lang) {
  if (lang && hljs.getLanguage(lang)) {
    // https://github.com/highlightjs/highlight.js/issues/2277
    return hljs.highlight(str, { language: lang, ignoreIllegals: true }).value;
  }

  return '';
};