《offline coolbook》笔记

https://jakearchibald.com/2014/offline-cookbook/

在install中对依赖进行缓存

self.addEventListener('install', function(event) {
  event.waitUntil(
    caches.open('mysite-static-v3').then(function(cache) {
      return cache.addAll([
        '/css/whatever-v3.css',
        '/css/imgs/sprites-v6.png',
        '/css/fonts/whatever-v8.woff',
        '/js/all-min-v4.js'
        // etc
      ]);
    })
  );
});

 　　waitUntil接收的参数是一个promise，这个promise决定了install阶段的持续时长和是否成功。

 在install中对非依赖进行缓存

self.addEventListener('install', function(event) {
  event.waitUntil(
    caches.open('mygame-core-v1').then(function(cache) {
      cache.addAll(
        // levels 11-20
      );
      return cache.addAll(
        // core assets & levels 1-10
      );
    })
  );
});

　　以上waitUntil接收到的promise，仅仅是对应加载了核心的缓存。虽然也加载了非关键的缓存（levels11-20），但是对install的状态无影响。

在activate阶段清除缓存

self.addEventListener('activate', function(event) {
  event.waitUntil(
    caches.keys().then(function(cacheNames) {
      return Promise.all(
        cacheNames.filter(function(cacheName) {
          // Return true if you want to remove this cache,
          // but remember that caches are shared across
          // the whole origin
        }).map(function(cacheName) {
          return caches.delete(cacheName);
        })
      );
    })
  );
});

　　Keep your activation as lean as possible, only use it for things you couldn't do while the old version was active

 处理用户的交互

　　给用户一个按钮，让用户选择保存某些资源以离线访问。资源的唯一标识与某个cache要一一对应

document.querySelector('.cache-article').addEventListener('click', function(event) {
  event.preventDefault();

  var id = this.dataset.articleId;
  caches.open('mysite-article-' + id).then(function(cache) {
    fetch('/get-article-urls?id=' + id).then(function(response) {
      // /get-article-urls returns a JSON-encoded array of
      // resource URLs that a given article depends on
      return response.json();
    }).then(function(urls) {
      cache.addAll(urls);
    });
  });
});

 　　以上代码与sw是否被激活无关。也就是说cache和sw的运行是分开的两部分。

拦截网络请求

　　当一个请求的响应不在cache中，就从网络获取，显示到界面上，最后保存到cache中。

self.addEventListener('fetch', function(event) {
  event.respondWith(
    caches.open('mysite-dynamic').then(function(cache) {
      return cache.match(event.request).then(function (response) {
        return response || fetch(event.request).then(function(response) {
          cache.put(event.request, response.clone());
          return response;
        });
      });
    })
  );
});

　　以上的clone是为了让页面对response的读取与cache对response的读取分离开来，互不影响。

更新cache

　　总是先更新缓存

self.addEventListener('fetch', function(event) {
  event.respondWith(
    caches.open('mysite-dynamic').then(function(cache) {
      return cache.match(event.request).then(function(response) {
        var fetchPromise = fetch(event.request).then(function(networkResponse) {
          cache.put(event.request, networkResponse.clone());
          return networkResponse;
        })
        return response || fetchPromise;
      })
    })
  );
});

消息推送

后台同步

只使用缓存

self.addEventListener('fetch', function(event) {
  // If a match isn't found in the cache, the response
  // will look like a connection error
  event.respondWith(caches.match(event.request));
});

只使用网络

self.addEventListener('fetch', function(event) {
  event.respondWith(fetch(event.request));
  // or simply don't call event.respondWith, which
  // will result in default browser behaviour
});

缓存优先，后访问网络

self.addEventListener('fetch', function(event) {
  event.respondWith(
    caches.match(event.request).then(function(response) {
      return response || fetch(event.request);
    })
  );
})

访问缓存和访问网络同时开始

　　对于某些情况，古老的硬盘+病毒扫描软件+快速的网络。访问网络的速度可能比访问硬盘更快。

self.addEventListener('fetch', function(event) {
  event.respondWith(
    promiseAny([
      caches.match(event.request),
      fetch(event.request)
    ])
  );
});

访问网络失败后才取缓存

self.addEventListener('fetch', function(event) {
  event.respondWith(
    fetch(event.request).catch(function() {
      return caches.match(event.request);
    })
  );
});

　　用于资源经常更新的站点，当离线访问时才使用旧的资源。

访问缓存后再访问网络

var networkDataReceived = false;

startSpinner();

// fetch fresh data
var networkUpdate = fetch('/data.json').then(function(response) {
  return response.json();
}).then(function(data) {
  networkDataReceived = true;
  updatePage();
});

// fetch cached data
caches.match('/data.json').then(function(response) {
  if (!response) throw Error("No data");
  return response.json();
}).then(function(data) {
  // don't overwrite newer network data
  if (!networkDataReceived) {
    updatePage(data);
  }
}).catch(function() {
  // we didn't get cached data, the network is our last hope:
  return networkUpdate;
}).catch(showErrorMessage).then(stopSpinner);

generic fallback

self.addEventListener('fetch', function(event) {
  event.respondWith(
    // Try the cache
    caches.match(event.request).then(function(response) {
      // Fall back to network
      return response || fetch(event.request);
    }).catch(function() {
      // If both fail, show a generic fallback:
      return caches.match('/offline.html');
      // However, in reality you'd have many different
      // fallbacks, depending on URL & headers.
      // Eg, a fallback silhouette image for avatars.
    })
  );
});

模板

importScripts('templating-engine.js');

self.addEventListener('fetch', function(event) {
  var requestURL = new URL(event.request);

  event.respondWith(
    Promise.all([
      caches.match('/article-template.html').then(function(response) {
        return response.text();
      }),
      caches.match(requestURL.path + '.json').then(function(response) {
        return response.json();
      })
    ]).then(function(responses) {
      var template = responses[0];
      var data = responses[1];

      return new Response(renderTemplate(template, data), {
        headers: {
          'Content-Type': 'text/html'
        }
      });
    })
  );
});

　　大概意思就是app shell缓存在本地，然后请求动态数据，两者渲染，得出结果。

将以上的技巧组合到一起

install阶段进行资源缓存

访问网络后对资源进行缓存

访问资源时，缓存优先，找不到后再访问网络

访问缓存后再访问网络来更新数据

self.addEventListener('fetch', function(event) {
  // Parse the URL:
  var requestURL = new URL(event.request.url);

  // Handle requests to a particular host specifically
  if (requestURL.hostname == 'api.example.com') {
    event.respondWith(/* some combination of patterns */);
    return;
  }
  // Routing for local URLs
  if (requestURL.origin == location.origin) {
    // Handle article URLs
    if (/^\/article\//.test(requestURL.pathname)) {
      event.respondWith(/* some other combination of patterns */);
      return;
    }
    if (/\.webp$/.test(requestURL.pathname)) {
      event.respondWith(/* some other combination of patterns */);
      return;
    }
    if (request.method == 'POST') {
      event.respondWith(/* some other combination of patterns */);
      return;
    }
    if (/cheese/.test(requestURL.pathname)) {
      event.respondWith(
        new Response("Flagrant cheese error", {
          status: 512
        })
      );
      return;
    }
  }

  // A sensible default pattern
  event.respondWith(
    caches.match(event.request).then(function(response) {
      return response || fetch(event.request);
    })
  );
});

完。