Service Workers is coming. Bring your own magic with the first programmable cache in your script, and more!
Presented at the GDG Korea DevFest 2014 on the 31st of May 2014: https://sites.google.com/site/gdgdevfestkorea2014/
3. Service Workers solve ..
● Offline usage
○ Offline-first
○ Sorry, no magic. Create your own!
■ Programmable cache control
■ Custom response - Constructor, IDB, etc.
● Background processing
○ Wanna do things while UA’s not running?
○ Push messages, Alarms (Task Scheduler),
BackgroundSync, etc.
6. ● Lifecycle events
Principles and Terms
● Runs on same origin
● Registration keyed by URL scope
● Document is controlled by matching SW
upon navigation
● Successfully installed worker is considered
worker in waiting
● Functional events
12. // scope defaults to "/*"
navigator.serviceWorker.register("/assets/v1/serviceworker.js").then(
function(serviceWorker) {
console.log("success!");
serviceWorker.postMessage("Howdy from your installing page.");
// To use the serviceWorker immediately, you might call
// window.location.reload()
}, function(why) {
console.error("Installing the worker failed!", why);
});
Registration
● In the page
“/*” /assets/v1/serviceworker.js
[ Registration map ]
Scope Script URL
Service Worker Lifecycle
13. Registration
● In the page
navigator.serviceWorker.register("/sw.js");
“/*” /sw.js
[ Registration map ]
Scope Script URL
“/foo/*” /foo/sw.js
“/*” /bar/sw.js
Service Worker Lifecycle
navigator.serviceWorker.register("/foo/sw.js", { scope: “/foo/*” });
navigator.serviceWorker.register("/bar/sw.js");
14. Installation
● Registration triggers installation of the SW
● UA fires install event to the installing
Service Worker
● The event handler may extend the lifetime
of SW for preparing its caches
Service Worker Lifecycle
15. Installation: oninstall
● In the Service Worker context
// caching.js
this.addEventListener("install", function(e) {
// Create a cache of resources. Begins the process of fetching them.
var shellResources = new Cache();
// The coast is only clear when all the resources are ready.
e.waitUntil(shellResources.add(
"/app.html",
"/assets/v1/base.css",
"/assets/v1/app.js",
"/assets/v1/logo.png",
"/assets/v1/intro_video.webm",
));
// Add Cache to the global so it can be used later during onfetch
self.caches.set("shell-v1", shellResources);
});
Service Worker Lifecycle
16. Programmable cache control
● new Cache()
[Constructor]
interface Cache {
Promise<AbstractResponse>
match((Request or ScalarValueString) request, optional QueryParams params);
Promise<sequence<AbstractResponse>>
matchAll((Request or ScalarValueString) request, optional QueryParams params);
Promise<any> add((Request or ScalarValueString)... requests);
Promise<any> put((Request or ScalarValueString) request, AbstractResponse response);
Promise<any>
delete((Request or ScalarValueString) request, optional QueryParams params);
Promise<any> each(CacheIterationCallback callback, optional object thisArg);
};
Service Worker Lifecycle
17. ● Worker in waiting
○ Once self.oninstall() ends
○ So to speak, the installation successfully done
○ This is not yet controlling the documents in scope
● navigator.serviceWorker.controller
○ When all the active documents in scope unload
○ The worker in waiting becomes active worker
○ self.clients.reloadAll() works
○ event.replace() works
Have a controller yet?
Service Worker Lifecycle
18. ● In the Service Worker context
this.addEventListener("fetch", function(e) {
// No "onfetch" events are dispatched to the ServiceWorker until it
// successfully installs.
// All operations on caches are async, including matching URLs, so we use
// Promises heavily. e.respondWith() even takes Promises to enable this:
e.respondWith(
caches.match(e.request).catch(function() {
return e.default();
}).catch(function() {
return caches.match("/fallback.html");
})
);
});
Handle a fetch: onfetch
Functional event processing
23. Security
● Origin relativity
● Cross origin resource
● HTTPS-only?
○ Protect end users from man-in-the-middle attacks
○ Existing "playground" services (e.g. github.io) now
work with HTTPS
○ HTTPS is coming across much more of the web
quickly
○ Devtools can loosen the restriction for development
24. ● Event-driven workers
○ Free to shutdown the worker when handler’s done
○ “Write your workers as though they will die after
every request”
● Keep the onactivate short
● Platform considerations
○ Enhance matching navigation
○ Events implicitly filter
○ Enhance startup
Performance
25. Is it ready for you?
● Chrome Canary
○ Partial under flag
○ chrome://flags/#enable-service-worker
● Firefox Nightly
○ Partial under flag
○ about:config > dom.serviceWorkers.enabled
● Stay alerted!
○ Jake’s “Is ServiceWorker ready?”
26. References and Practices
● Service Worker - first draft published - Jake
Archibald
● Specification
● Github’s explainer
● Github’s implementation considerations
