本文发表在 rolia.net 枫下论坛function installStaticFiles() {

return caches.open(CACHE)
.then(cache => {

// cache desirable files
cache.addAll(installFilesDesirable);

// cache essential files
return cache.addAll(installFilesEssential);

});

}

// clear old caches
function clearOldCaches() {

return caches.keys()
.then(keylist => {

return Promise.all(
keylist
.filter(key => key !== CACHE)
.map(key => caches.delete(key))
);

});

}

// application installation
self.addEventListener('install', event => {

console.log('service worker: install');

// cache core files
event.waitUntil(
installStaticFiles()
.then(() => self.skipWaiting())
);

});


// application activated
self.addEventListener('activate', event => {

console.log('service worker: activate');

// delete old caches
event.waitUntil(
clearOldCaches()
.then(() => self.clients.claim())
);

});


// is image URL?
function isImage(url) {
var iExt = ['png', 'jpg', 'jpeg', 'gif', 'webp', 'bmp'].map(f => '.' + f);
return iExt.reduce((ret, ext) => ret || url.endsWith(ext), false);

}

function isCacheable(url) {
if (url.substr(url.indexOf("/", 10)) == "/")
return true;
if (url.indexOf("/upImg/") != -1)
return false;
if (isImage(url))
return true;
var iExt = ['js', 'css'].map(f => '.' + f);
return iExt.reduce((ret, ext) => ret || url.endsWith(ext), false);
}

// return offline asset
function offlineAsset(url) {

if (isImage(url)) {

// return image
return new Response(
'<svg role="img" viewBox="0 0 400 300" xmlns="http://www.w3.org/2000/svg"><title>offline</title><path d="M0 0h400v300H0z" fill="#eee" /><text x="200" y="150" text-anchor="middle" dominant-baseline="middle" font-family="sans-serif" font-size="50" fill="#ccc">offline</text></svg>', {
headers: {
'Content-Type': 'image/svg+xml',
'Cache-Control': 'no-store'
}
}
);
} else if (url.endsWith(".js")) {
return caches.match(offlineJs);
} else {

// return page
return caches.match(offlineHtml);

}

}


// application fetch network data
self.addEventListener('fetch', event => {

// abandon non-GET requests
if (event.request.method !== 'GET') return;

let url = event.request.url;

if (isCacheable(url)) {
event.respondWith(
caches.open(CACHE)
.then(cache => {
return cache.match(event.request)
.then(response => {
if (response) {
// return cached file
//console.log('cache fetch: ' + url);
return response;
}

// make network request
return fetch(event.request)
.then(newreq => {
//console.log('network fetch: ' + url);
if (newreq.ok) cache.put(event.request, newreq.clone());
return newreq;
})
// app is offline
.catch(() => offlineAsset(url));
});
})
);
} else {
event.respondWith(
caches.open(CACHE)
.then(cache => {
return cache.match(event.request)
.then(response => {
// make network request
return fetch(event.request)
.then(newreq => {
return newreq;
})
// app is offline
.catch(() => offlineAsset(url));
});
})
);

}
});更多精彩文章及讨论，请光临枫下论坛 rolia.net