《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
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。
