sw.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',
 'unpkg.com'
]

// The Util Function to hack URLs of intercepted requests
const getFixedUrl = (req) => {
 var now = Date.now()
 var 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
 if (url.hostname === self.location.hostname) {
 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 */ })
 )
 }
})