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",
  "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 */
        })
    );
  }
});