动态prefetch下个页面的资源，提升用户首次体验。

prefetch.js

requestIdleCallback(() => {
  fetch("xxx/a.html").then(res => res.text()).then(html => {
    const reg = /target*.js/gi;
    const scripts = html.match(reg);
    if(scripts && scripts.length) {
      scripts.forEach(src => {
        const link = document.createElement("link");
        link.rel = "prefetch";
        link.href = src;
        document.head.appendChild(link);
      });
    }
  })
}, { timeout: 1000 * 5 })