114 lines
3.9 KiB
Markdown
114 lines
3.9 KiB
Markdown
# 离线模式
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[Progressive Web Apps](https://developers.google.com/web/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。
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要使用它也非常容易。
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## 创建 serviceWorker
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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。
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*sw.js*
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```js
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/* ===========================================================
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* docsify sw.js
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* ===========================================================
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* Copyright 2016 @huxpro
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* Licensed under Apache 2.0
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* Register service worker.
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* ========================================================== */
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const RUNTIME = 'docsify'
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const HOSTNAME_WHITELIST = [
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self.location.hostname,
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'fonts.gstatic.com',
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'fonts.googleapis.com',
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'cdn.jsdelivr.net'
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]
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// The Util Function to hack URLs of intercepted requests
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const getFixedUrl = (req) => {
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var now = Date.now()
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var url = new URL(req.url)
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// 1. fixed http URL
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// Just keep syncing with location.protocol
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// fetch(httpURL) belongs to active mixed content.
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// And fetch(httpRequest) is not supported yet.
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url.protocol = self.location.protocol
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// 2. add query for caching-busting.
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// Github Pages served with Cache-Control: max-age=600
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// max-age on mutable content is error-prone, with SW life of bugs can even extend.
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// Until cache mode of Fetch API landed, we have to workaround cache-busting with query string.
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// Cache-Control-Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=453190
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if (url.hostname === self.location.hostname) {
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url.search += (url.search ? '&' : '?') + 'cache-bust=' + now
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}
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return url.href
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}
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/**
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* @Lifecycle Activate
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* New one activated when old isnt being used.
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*
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* waitUntil(): activating ====> activated
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*/
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self.addEventListener('activate', event => {
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event.waitUntil(self.clients.claim())
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})
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/**
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* @Functional Fetch
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* All network requests are being intercepted here.
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*
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* void respondWith(Promise<Response> r)
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*/
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self.addEventListener('fetch', event => {
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// Skip some of cross-origin requests, like those for Google Analytics.
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if (HOSTNAME_WHITELIST.indexOf(new URL(event.request.url).hostname) > -1) {
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// Stale-while-revalidate
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// similar to HTTP's stale-while-revalidate: https://www.mnot.net/blog/2007/12/12/stale
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// Upgrade from Jake's to Surma's: https://gist.github.com/surma/eb441223daaedf880801ad80006389f1
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const cached = caches.match(event.request)
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const fixedUrl = getFixedUrl(event.request)
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const fetched = fetch(fixedUrl, { cache: 'no-store' })
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const fetchedCopy = fetched.then(resp => resp.clone())
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// Call respondWith() with whatever we get first.
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// If the fetch fails (e.g disconnected), wait for the cache.
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// If there’s nothing in cache, wait for the fetch.
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// If neither yields a response, return offline pages.
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event.respondWith(
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Promise.race([fetched.catch(_ => cached), cached])
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.then(resp => resp || fetched)
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.catch(_ => { /* eat any errors */ })
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)
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// Update the cache with the version we fetched (only for ok status)
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event.waitUntil(
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Promise.all([fetchedCopy, caches.open(RUNTIME)])
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.then(([response, cache]) => response.ok && cache.put(event.request, response))
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.catch(_ => { /* eat any errors */ })
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)
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}
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})
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```
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## 注册
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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。
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*index.html*
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```html
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<script>
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if (typeof navigator.serviceWorker !== 'undefined') {
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navigator.serviceWorker.register('sw.js')
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}
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</script>
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```
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## 体验一下
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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。
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