New improvements for web developers - Promises, fetch, Service Workers, Push notifications, Add to Homescreen. Slides from a talk I gave at #frontendfi in Helsinki yesterday

1. Web improvements @robertnyman

2. Promises

4. fulfilled = The action relating to the promise succeeded
rejected = The action relating to the promise failed
pending = Hasn't fulfilled or rejected yet
settled = Has fulfilled or rejected

5. var promise = new Promise(function(resolve, reject) {
// do a thing, possibly async, then…
if (/* everything turned out fine */) {
resolve("Stuff worked!");
}
else {
reject(Error("It broke"));
}
});

6. promise.then(function(result) {
console.log(result); // "Stuff worked!"
}, function(err) {
console.log(err); // Error: "It broke"
});

7. fetch()

8. XMLHttpRequest example
function reqListener() {
var data = JSON.parse(this.responseText);
console.log(data);
}
function reqError(err) {
console.log('Fetch Error :-S', err);
}
var oReq = new XMLHttpRequest();
oReq.onload = reqListener;
oReq.onerror = reqError;
oReq.open('get', './api/some.json', true);
oReq.send();

9. fetch() version
fetch('./api/some.json')
.then(
function(response) {
if (response.status !== 200) {
console.log('Looks like there was a problem. Status Code: ' +
response.status);
return;
}
// Examine the text in the response
response.json().then(function(data) {
console.log(data);
});
}
)
.catch(function(err) {
console.log('Fetch Error :-S', err);
});

10. Response metadata
fetch('users.json').then(function(response) {
console.log(response.headers.get('Content-Type'));
console.log(response.headers.get('Date'));
console.log(response.status);
console.log(response.statusText);
console.log(response.type);
console.log(response.url);
});

11. Response Types
basic
cors
opaque

12. Defining modes
same-origin
cors
cors-with-forced-preflight
no-cors

13. Defining modes
fetch('http://some-site.com/cors-enabled/some.json', {mode: 'cors'})
.then(function(response) {
return response.text();
})
.then(function(text) {
console.log('Request successful', text);
})
.catch(function(error) {
log('Request failed', error)
});

14. Service Workers

15. It's a JavaScript Worker, so it can't access the DOM
directly. Instead responds to postMessages
Service worker is a programmable network proxy
It will be terminated when not in use, and restarted
when it's next needed
Makes extensive use of Promises

17. No Service Worker

18. HTTPS is Needed

19. Register and Installing a Service Worker
if ('serviceWorker' in navigator) {
navigator.serviceWorker.register('/sw.js').then(function(registration) {
// Registration was successful
console.log('ServiceWorker registration successful with scope: ',
registration.scope);
}).catch(function(err) {
// registration failed :(
console.log('ServiceWorker registration failed: ', err);
});
}

20. chrome://inspect/#service-workers

21. // The files we want to cache
var urlsToCache = [
'/',
'/styles/main.css',
'/script/main.js'
];
// Set the callback for the install step
self.addEventListener('install', function(event) {
// Perform install steps
});
Installing

22. Inside our install callback:
1. Open a cache
2. Cache our files
3. Confirm whether all the required
assets are cached or not

23. Install callback
var CACHE_NAME = 'my-site-cache-v1';
var urlsToCache = [
'/',
'/styles/main.css',
'/script/main.js'
];
self.addEventListener('install', function(event) {
// Perform install steps
event.waitUntil(
caches.open(CACHE_NAME)
.then(function(cache) {
console.log('Opened cache');
return cache.addAll(urlsToCache);
})
);
});

24. self.addEventListener('fetch', function(event) {
event.respondWith(
caches.match(event.request)
.then(function(response) {
// Cache hit - return response
if (response) {
return response;
}
return fetch(event.request);
}
)
);
});
Caching and Returning Requests

25. self.addEventListener('fetch', function(event) {
event.respondWith(
caches.match(event.request)
.then(function(response) {
// Cache hit - return response
if (response) {
return response;
}
// IMPORTANT: Clone the request. A request is a stream and
// can only be consumed once. Since we are consuming this
// once by cache and once by the browser for fetch, we need
// to clone the response
var fetchRequest = event.request.clone();
return fetch(fetchRequest).then(
function(response) {
// Check if we received a valid response
if(!response || response.status !== 200 || response.type !== 'basic') {
return response;
}
// IMPORTANT: Clone the response. A response is a stream
// and because we want the browser to consume the response
// as well as the cache consuming the response, we need
// to clone it so we have 2 stream.
var responseToCache = response.clone();
caches.open(CACHE_NAME)
.then(function(cache) {
cache.put(event.request, responseToCache);
});
return response;
}
);
})
);
});
Caching new requests cumulatively

26. Updating a Service Worker

27. 1. Update your service worker JavaScript file.
2. Your new service worker will be started and the
install event will be fired.
3. New Service Worker will enter a "waiting" state
4. When open pages are closed, the old Service
Worker will be killed - new service worker will take
control.
5. Once new Service Worker takes control, its
activate event will be fired.
Updating a Service Worker

28. Cache management & whitelists
self.addEventListener('activate', function(event) {
var cacheWhitelist = ['pages-cache-v1', 'blog-posts-cache-v1'];
event.waitUntil(
caches.keys().then(function(cacheNames) {
return Promise.all(
cacheNames.map(function(cacheName) {
if (cacheWhitelist.indexOf(cacheName) === -1) {
return caches.delete(cacheName);
}
})
);
})
);
});

29. Push notifications

31. <button class="js-push-button" disabled>
Enable Push Messages
</button>

32. // Are Notifications supported in the service worker?
if (!('showNotification' in ServiceWorkerRegistration.prototype)) {
console.warn('Notifications aren't supported.');
return;
}

33. // Check the current Notification permission.
// If its denied, it's a permanent block until the
// user changes the permission
if (Notification.permission === 'denied') {
console.warn('The user has blocked notifications.');
return;
}

34. // Check if push messaging is supported
if (!('PushManager' in window)) {
console.warn('Push messaging isn't supported.');
return;
}

35. // We need the service worker registration to check for a subscription
navigator.serviceWorker.ready.then(function(serviceWorkerRegistration) {
// Do we already have a push message subscription?
serviceWorkerRegistration.pushManager.getSubscription()
.then(function(subscription) {
// Enable any UI which subscribes / unsubscribes from
// push messages.
var pushButton = document.querySelector('.js-push-button');
pushButton.disabled = false;
if (!subscription) {
// We aren't subscribed to push, so set UI
// to allow the user to enable push
return;
}
// Keep your server in sync with the latest subscriptionId
sendSubscriptionToServer(subscription);
// Set your UI to show they have subscribed for
// push messages
pushButton.textContent = 'Disable Push Messages';
isPushEnabled = true;
})
.catch(function(err) {
console.warn('Error during getSubscription()', err);
});
});

36. {
"name": "Push Demo",
"short_name": "Push Demo",
"icons": [{
"src": "images/icon-192x192.png",
"sizes": "192x192",
"type": "image/png"
}],
"start_url": "/index.html?homescreen=1",
"display": "standalone",
"gcm_sender_id": "123456789012",
"gcm_user_visible_only": true
}
<link rel="manifest" href="manifest.json">

37. Add to
Homescreen

38. Cache management & whitelistsApp Install Banners

39. App Install Banners prerequisites
You have a web app manifest file
You have a service worker registered on
your site. We recommend a simple custom
offline page service worker
Your site is served over HTTPS (you need a
service worker after all)
The user has visited your site twice over
two separate days during the course of two
weeks.

40. "You can do all of this?"

42. Robert Nyman
robertnyman.com
rnyman@google.com
Google
@robertnyman