离线模式

Progressive Web Apps(PWA) 是一项融合 Web 和 Native 应用各项优点的解决方案。我们可以利用其支持离线功能的特点，让我们的网站可以在信号差或者离线状态下正常运行。
要使用它也非常容易。

创建 serviceWorker

这里已经整理好了一份代码，你只需要在网站根目录下创建一个 sw.js 文件，并粘贴下面的代码。

sw.js

  1. /* ===========================================================
  2.  * docsify sw.js
  3.  * ===========================================================
  4.  * Copyright 2016 @huxpro
  5.  * Licensed under Apache 2.0
  6.  * Register service worker.
  7.  * ========================================================== */
  9. const RUNTIME = 'docsify'
  10. const HOSTNAME_WHITELIST = [
  11.   self.location.hostname,
  12.   'fonts.gstatic.com',
  13.   'fonts.googleapis.com',
  14.   'unpkg.com'
  15. ]
  17. // The Util Function to hack URLs of intercepted requests
  18. const getFixedUrl = (req) => {
  19.   var now = Date.now()
  20.   var url = new URL(req.url)
  22.   // 1. fixed http URL
  23.   // Just keep syncing with location.protocol
  24.   // fetch(httpURL) belongs to active mixed content.
  25.   // And fetch(httpRequest) is not supported yet.
  26.   url.protocol = self.location.protocol
  28.   // 2. add query for caching-busting.
  29.   // Github Pages served with Cache-Control: max-age=600
  30.   // max-age on mutable content is error-prone, with SW life of bugs can even extend.
  31.   // Until cache mode of Fetch API landed, we have to workaround cache-busting with query string.
  32.   // Cache-Control-Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=453190
  33.   if (url.hostname === self.location.hostname) {
  34.     url.search += (url.search ? '&' : '?') + 'cache-bust=' + now
  35.   }
  36.   return url.href
  37. }
  39. /**
  40.  *  @Lifecycle Activate
  41.  *  New one activated when old isnt being used.
  42.  *
  43.  *  waitUntil(): activating ====> activated
  44.  */
  45. self.addEventListener('activate', event => {
  46.   event.waitUntil(self.clients.claim())
  47. })
  49. /**
  50.  *  @Functional Fetch
  51.  *  All network requests are being intercepted here.
  52.  *
  53.  *  void respondWith(Promise<Response> r)
  54.  */
  55. self.addEventListener('fetch', event => {
  56.   // Skip some of cross-origin requests, like those for Google Analytics.
  57.   if (HOSTNAME_WHITELIST.indexOf(new URL(event.request.url).hostname) > -1) {
  58.     // Stale-while-revalidate
  59.     // similar to HTTP's stale-while-revalidate: https://www.mnot.net/blog/2007/12/12/stale
  60.     // Upgrade from Jake's to Surma's: https://gist.github.com/surma/eb441223daaedf880801ad80006389f1
  61.     const cached = caches.match(event.request)
  62.     const fixedUrl = getFixedUrl(event.request)
  63.     const fetched = fetch(fixedUrl, { cache: 'no-store' })
  64.     const fetchedCopy = fetched.then(resp => resp.clone())
  66.     // Call respondWith() with whatever we get first.
  67.     // If the fetch fails (e.g disconnected), wait for the cache.
  68.     // If there’s nothing in cache, wait for the fetch.
  69.     // If neither yields a response, return offline pages.
  70.     event.respondWith(
  71.       Promise.race([fetched.catch(_ => cached), cached])
  72.         .then(resp => resp || fetched)
  73.         .catch(_ => { /* eat any errors */ })
  74.     )
  76.     // Update the cache with the version we fetched (only for ok status)
  77.     event.waitUntil(
  78.       Promise.all([fetchedCopy, caches.open(RUNTIME)])
  79.         .then(([response, cache]) => response.ok && cache.put(event.request, response))
  80.         .catch(_ => { /* eat any errors */ })
  81.     )
  82.   }
  83. })

注册

现在，到 index.html 里注册它。这个功能只能工作在一些现代浏览器上，所以我们需要加个判断。

index.html

  1. <script>
  2.   if (typeof navigator.serviceWorker !== 'undefined') {
  3.     navigator.serviceWorker.register('sw.js')
  4.   }
  5. </script>

体验一下

发布你的网站，并开始享受离线模式的魔力吧！:ghost: 当然你现在看到的 docsify 的文档网站已经支持离线模式了，你可以关掉 Wi-Fi 体验一下。