pwa.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',
    'cdn.jsdelivr.net'
]

// 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 */ })
        )
    }
})