docs(pwa): add pwa

docs/_sidebar.md

@@ -16,5 +16,6 @@
  - [Helpers](/helpers)
  - [Vue compatibility](/vue)
  - [CDN](/cdn)
+ - [Offline Mode(PWA)<sup style="color: #F44336;">new</sup>](/pwa)
 
 - [Changelog](/changelog)

docs/pwa.md

@@ -0,0 +1,111 @@
+# Offline Mode
+
+[Progressive Web Apps](https://developers.google.com/web/progressive-web-apps/)(PWA) are experiences that combine the best of the web and the best of apps. we can enhance our website with service workers to work **offline** or on low-quality networks.
+It is also very easy to use it.
+
+## Create serverWorker
+Create a sw.js file in your documents root directory and copy this code.
+
+*sw.js*
+
+```js
+/* ===========================================================
+ * docsify sw.js
+ * ===========================================================
+ * Copyright 2016 @huxpro
+ * Licensed under Apache 2.0
+ * Register service worker.
+ * ========================================================== */
+
+const RUNTIME = 'docsify';
+const HOSTNAME_WHITELIST = [
+  self.location.hostname,
+  'fonts.gstatic.com',
+  'fonts.googleapis.com'
+]
+
+// The Util Function to hack URLs of intercepted requests
+const getFixedUrl = (req) => {
+  var now = Date.now();
+  url = new URL(req.url)
+
+  // 1. fixed http URL
+  // Just keep syncing with location.protocol
+  // fetch(httpURL) belongs to active mixed content.
+  // And fetch(httpRequest) is not supported yet.
+  url.protocol = self.location.protocol
+
+  // 2. add query for caching-busting.
+  // Github Pages served with Cache-Control: max-age=600
+  // max-age on mutable content is error-prone, with SW life of bugs can even extend.
+  // Until cache mode of Fetch API landed, we have to workaround cache-busting with query string.
+  // Cache-Control-Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=453190
+  url.search += (url.search ? '&' : '?') + 'cache-bust=' + now;
+  return url.href
+}
+
+/**
+ *  @Lifecycle Activate
+ *  New one activated when old isnt being used.
+ *
+ *  waitUntil(): activating ====> activated
+ */
+self.addEventListener('activate',  event => {
+  event.waitUntil(self.clients.claim());
+});
+
+
+/**
+ *  @Functional Fetch
+ *  All network requests are being intercepted here.
+ *
+ *  void respondWith(Promise<Response> r);
+ */
+self.addEventListener('fetch', event => {
+  // Skip some of cross-origin requests, like those for Google Analytics.
+  if (HOSTNAME_WHITELIST.indexOf(new URL(event.request.url).hostname) > -1) {
+    // Stale-while-revalidate
+    // similar to HTTP's stale-while-revalidate: https://www.mnot.net/blog/2007/12/12/stale
+    // Upgrade from Jake's to Surma's: https://gist.github.com/surma/eb441223daaedf880801ad80006389f1
+    const cached = caches.match(event.request);
+    const fixedUrl = getFixedUrl(event.request);
+    const fetched = fetch(fixedUrl, {cache: 'no-store'});
+    const fetchedCopy = fetched.then(resp => resp.clone());
+
+    // Call respondWith() with whatever we get first.
+    // If the fetch fails (e.g disconnected), wait for the cache.
+    // If there’s nothing in cache, wait for the fetch.
+    // If neither yields a response, return offline pages.
+    event.respondWith(
+      Promise.race([fetched.catch(_ => cached), cached])
+        .then(resp => resp || fetched)
+        .catch(_ => {/* eat any errors */})
+    );
+
+    // Update the cache with the version we fetched (only for ok status)
+    event.waitUntil(
+      Promise.all([fetchedCopy, caches.open(RUNTIME)])
+        .then(([response, cache]) => response.ok && cache.put(event.request, response))
+        .catch(_ => {/* eat any errors */})
+    );
+  }
+});
+```
+
+## Register
+
+Now, register it in your `index.html`. It only works on some modern browsers, so we need to judge.
+
+*index.html*
+
+```html
+<script>
+  if (typeof navigator.serviceWorker !== 'undefined') {
+    navigator.serviceWorker.register('sw.js')
+  }
+</script>
+```
+
+## Enjoy it
+
+Release your website and start experiencing magical offline feature. :ghost: You can turn off Wi-Fi and refresh the current site to experience it.

docs/zh-cn/_sidebar.md

@@ -16,5 +16,6 @@
  - [文档助手](zh-cn/helpers)
  - [兼容 Vue](zh-cn/vue)
  - [CDN](zh-cn/cdn)
+ - [离线模式(PWA)<sup style="color: #F44336;">new</sup>](zh-cn/pwa)
 
 - [Changelog](zh-cn/changelog)

docs/zh-cn/pwa.md

@@ -0,0 +1,111 @@
+# 离线模式
+
+[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。
+要使用它也非常容易。
+
+## 创建 serverWorker
+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，并张贴下面的代码。
+
+*sw.js*
+
+```js
+/* ===========================================================
+ * docsify sw.js
+ * ===========================================================
+ * Copyright 2016 @huxpro
+ * Licensed under Apache 2.0
+ * Register service worker.
+ * ========================================================== */
+
+const RUNTIME = 'docsify';
+const HOSTNAME_WHITELIST = [
+  self.location.hostname,
+  'fonts.gstatic.com',
+  'fonts.googleapis.com'
+]
+
+// The Util Function to hack URLs of intercepted requests
+const getFixedUrl = (req) => {
+  var now = Date.now();
+  url = new URL(req.url)
+
+  // 1. fixed http URL
+  // Just keep syncing with location.protocol
+  // fetch(httpURL) belongs to active mixed content.
+  // And fetch(httpRequest) is not supported yet.
+  url.protocol = self.location.protocol
+
+  // 2. add query for caching-busting.
+  // Github Pages served with Cache-Control: max-age=600
+  // max-age on mutable content is error-prone, with SW life of bugs can even extend.
+  // Until cache mode of Fetch API landed, we have to workaround cache-busting with query string.
+  // Cache-Control-Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=453190
+  url.search += (url.search ? '&' : '?') + 'cache-bust=' + now;
+  return url.href
+}
+
+/**
+ *  @Lifecycle Activate
+ *  New one activated when old isnt being used.
+ *
+ *  waitUntil(): activating ====> activated
+ */
+self.addEventListener('activate',  event => {
+  event.waitUntil(self.clients.claim());
+});
+
+
+/**
+ *  @Functional Fetch
+ *  All network requests are being intercepted here.
+ *
+ *  void respondWith(Promise<Response> r);
+ */
+self.addEventListener('fetch', event => {
+  // Skip some of cross-origin requests, like those for Google Analytics.
+  if (HOSTNAME_WHITELIST.indexOf(new URL(event.request.url).hostname) > -1) {
+    // Stale-while-revalidate
+    // similar to HTTP's stale-while-revalidate: https://www.mnot.net/blog/2007/12/12/stale
+    // Upgrade from Jake's to Surma's: https://gist.github.com/surma/eb441223daaedf880801ad80006389f1
+    const cached = caches.match(event.request);
+    const fixedUrl = getFixedUrl(event.request);
+    const fetched = fetch(fixedUrl, {cache: 'no-store'});
+    const fetchedCopy = fetched.then(resp => resp.clone());
+
+    // Call respondWith() with whatever we get first.
+    // If the fetch fails (e.g disconnected), wait for the cache.
+    // If there’s nothing in cache, wait for the fetch.
+    // If neither yields a response, return offline pages.
+    event.respondWith(
+      Promise.race([fetched.catch(_ => cached), cached])
+        .then(resp => resp || fetched)
+        .catch(_ => {/* eat any errors */})
+    );
+
+    // Update the cache with the version we fetched (only for ok status)
+    event.waitUntil(
+      Promise.all([fetchedCopy, caches.open(RUNTIME)])
+        .then(([response, cache]) => response.ok && cache.put(event.request, response))
+        .catch(_ => {/* eat any errors */})
+    );
+  }
+});
+```
+
+## 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*
+
+```html
+<script>
+  if (typeof navigator.serviceWorker !== 'undefined') {
+    navigator.serviceWorker.register('sw.js')
+  }
+</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。