sw.js

---
layout: null
---

'use strict';

const staticCacheName = "version-{{site.time | date: '%Y%m%d%H%M%S'}}";
const pagesCacheName  = 'pages';
const imagesCacheName = 'images';

const cacheList = [
  staticCacheName,
  pagesCacheName,
  imagesCacheName
];

const offlinePages = [
    "/",
    {% for page in site.html_pages %}
    '{{ page.url | relative_url }}',
    {% endfor %}
    {% for post in site.posts limit:3 %}
    '{{ post.url | relative_url }}',
    {% endfor %}
];

function updateStaticCache() {
  return caches.open(staticCacheName)
}

function stashInCache(cacheName, request, response) {
  caches.open(cacheName)
    .then(cache => cache.put(request, response));
}

// Limit the number of items in a specified cache.
function trimCache(cacheName, maxItems) {
  caches.open(cacheName)
    .then(cache => {
      cache.keys()
        .then(keys => {
          if (keys.length > maxItems) {
            cache.delete(keys[0])
              .then(trimCache(cacheName, maxItems));
          }
        });
    });
}

// Remove caches whose name is no longer valid
function clearOldCaches() {
  return caches.keys()
    .then(keys => {
      return Promise.all(keys
        .filter(key => !cacheList.includes(key))
        .map(key => caches.delete(key))
      );
    });
}

self.addEventListener('install', event => {
  event.waitUntil(updateStaticCache()
    .then(() => self.skipWaiting())
  );
});

self.addEventListener('activate', event => {
  event.waitUntil(clearOldCaches()
    .then(() => self.clients.claim())
  );
  event.waitUntil(async function() {
    // Feature-detect
    if (self.registration.navigationPreload) {
      // Enable navigation preloads!
      await self.registration.navigationPreload.enable();
    }
  }());
});

self.addEventListener('message', event => {
  if (event.data.command == 'trimCaches') {
    trimCache(pagesCacheName, 35);
    trimCache(imagesCacheName, 20);
  }
});

self.addEventListener('fetch', event => {
  let request = event.request;
  let url = new URL(request.url);

  //Ignore non-GET requests
  if (request.method !== 'GET') {
    return;
  }

  // For HTML requests, try the network first, fall back to the cache, finally the offline page
  if (request.headers.get('Accept').includes('text/html')) {

    event.respondWith(
      fetch(request)
      .then(response => {
        // NETWORK
        // Stash a copy of this page in the pages cache
        let copy = response.clone();
        if (offlinePages.includes(url.pathname) || offlinePages.includes(url.pathname + '/')) {
          stashInCache(staticCacheName, request, copy);
        } else {
          stashInCache(pagesCacheName, request, copy);
        }
        return response;
      })
      .catch(() => {
        // CACHE or FALLBACK
        return caches.match(request)
          .then(response => response || caches.match('/offline/'));
      })
    );
    return;
  }

  // For non-HTML requests, look in the cache first, fall back to the network
  event.respondWith(
    caches.match(request)
    .then(response => {
      // CACHE
      return response || fetch(request)
        .then(response => {
          // NETWORK
          // If the request is for an image, stash a copy of this image in the images cache
          if (request.headers.get('Accept').includes('image')) {
            let copy = response.clone();
            stashInCache(imagesCacheName, request, copy);
          }
          return response;
        })
        .catch(() => {
          // OFFLINE
          // If the request is for an image, show an offline placeholder
          if (request.headers.get('Accept').includes('image')) {
            return new Response('<svg role="img" aria-labelledby="offline-title" viewBox="0 0 400 300" xmlns="http://www.w3.org/2000/svg"><title id="offline-title">Offline</title><g fill="none" fill-rule="evenodd"><path fill="#D8D8D8" d="M0 0h400v300H0z"/><text fill="#9B9B9B" font-family="Helvetica Neue,Arial,Helvetica,sans-serif" font-size="72" font-weight="bold"><tspan x="93" y="172">offline</tspan></text></g></svg>', {
              headers: {
                'Content-Type': 'image/svg+xml',
                'Cache-Control': 'no-store'
              }
            });
          }
        });
    })
  );
});