LDNWebPerf November 2016 - Peter O’Shaughnessy

Developing a progressive web app for Snapchat-like selfies has led me to learn about service worker practicalities, client-side image generation and standalone app limitations. I've come unstuck by a Chromium bug and sparked a WICG discussion. Combining the things I've learned along the way with advice I've received from Google…

1. Peter O'Shaughnessy @poshaughnessy @samsunginternet Progressive Web Apps Service Workers & Server-free Selfies !
6. Snapchat by Snap Inc. Not to be confused with... "
7. “PWAs combine the best of web & the best of native” #
8. Multi-platform Frictionless Discoverable Accessible Best of web $
9. Add to Home Screen Offline Instant load Push notifications Best of native %
10. “PWAs are all about removing friction” &
11. Service Workers '
12. var RESOURCES = ['/images/emojione/1f600.svg', ...]; self.addEventListener('install', function(event) { function onInstall () { return caches.open(CACHE_NAME) .then(function(cache) { return cache.addAll(RESOURCES); }); } ); ( Don't cache too much on install! ⚖
14. Emoji One SVGs (left), Unicode emojis (right)
15. gulp.task('generate-service-worker', function(callback) { swPrecache.write(path.join(rootDir, 'service-worker.js'), { staticFileGlobs: [rootDir + '/**/*.{js,html,css,svg}'], stripPrefix: rootDir }, callback); }); github.com/GoogleChrome/sw-precache * Automate precache resource list +
16. // sw.js import resources from '\0initial-resources'; ... cache.addAll( resources ); bit.ly/rollup-precache
17. const RESOURCES = [ '/', '/index.html', ... ]; ... cache.addAll( RESOURCES ); , URLs, not files -
18. . Remember to check Lighthouse /0
19. 1. SSR app shell & initial page. CSR takes over. 2. SSR only app shell. JS fetches rest on load. 3. SSR full page. 4. CSR full page. 5 Rendering preferences (in order) 1
20. “cache first”, then fallback to network toolbox.router.get('/images', toolbox.cacheFirst); 6 Easy caching strategies with sw-toolbox 2
21. “network first”, then fallback to cache toolbox.router.get('/api', toolbox.networkFirst);
22. “fastest” — serve whichever comes back first toolbox.router.get('/profile', toolbox.fastest); “network only” “cache only”
23. getUserMedia 3
24. ( Enhance progressively! 4
25. * Standalone & localhost: prompt doesn't appear 5
26. const constraints = { width: {ideal: width, max: width}, height: {ideal: height, max: height} }; navigator.mediaDevices.getUserMedia({video: constraints}) ... , Don't rely on getUserMedia constraints 6
27. Saving images 7
28. var link = document.createElement('a'); link.download = 'My Snapwat'; link.href = dataURI; link.click(); ( Common <a download> hack ⛏
29. * Data-uri downloads currently blocked ⛔
30. , <a download> requests bypass SW :
31. window.open(canvas.toDataURL('image/png'), '_blank'); 4 'New tab' in standalone mode kills page ;
32. 5 No long tap menu in standalone mode <
33. = Save image disabled if image too big >
34. bit.ly/save-image-feature Do we need a 'save image' feature? ?
35. <input type=”file”> orientation (I used JavaScript-Load- Image) Calculating canvas text bounds Text doesn't render when over ~240px? Other tricky things @
36. Next for Snapwat? ⏩
37. Push notifications B
38. Web Share API C
39. Head tracking D
40. Brushes E Undo/Redo ↩↪ Local storage? H Any suggestions...? I
41. Next for PWAs? J
42. Service worker & cache API improvements K
43. navigator.serviceWorker.ready.then(function(reg) { return reg.sync.register('syncTest'); }).then(function() { log('Sync registered'); }); Background sync ⛰
44. Link: </service-worker.js>; rel="serviceworker" Origin-Trial: token_obtained_from_signup bit.ly/foreign-fetch Foreign fetch ✈
45. jakearchibald.com/2016/service-worker-meeting-notes/ Multiple service workers for parallelisation? N
46. self.addEventListener('fetch', function(event) { if (event.request.headers.get('save-data')) { ... bit.ly/save-data-header Save-Data header O
47. P snapw.at Q github.com/SamsungInternet/snapwat
48. @poshaughnessy @samsunginternet github.com/samsunginternet medium.com/samsung-internet-dev Thanks! R