The document discusses the development of Flipkart Lite as a Progressive Web App (PWA) for mobile users in India, highlighting key considerations like performance, engagement, and security. It outlines implementation strategies involving service workers, caching, and analytics, while sharing lessons learned regarding effective caching, performance tracking, and handling cross-origin resource sharing (CORS). Future enhancements are also mentioned, such as HTTP2 and HTML streaming.

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Real World PWAs
(Building Flipkart Lite)
Abhinav Rastogi
@_abhinavrastogi

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Main Considerations

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Build for mobile India, run anywhere
Build for a complex eCommerce marketplace

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What we needed to do
(What is a Progressive Web App?)

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‣ performance as a feature
‣ immersive experience
‣ security
‣ solve for flaky networks
‣ engagement
‣ always up-to-date
What we needed to do

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How we achieved it

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How we achieved it
‣ service workers
‣ push notifications
‣ add to home screen, splash screen
‣ smooth animations (RAIL, FLIP)
‣ security (HTTPS, CSP)

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Client-side Apps
Single Page Apps

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Real world Service Workers!

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First thing: Kill Switch
(and versioning)

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self.addEventListener('install', event => {
event.waitUntil(self.skipWaiting());
});
self.addEventListener('activate', event => {
event.waitUntil(self.clients.claim());
});

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sw-toolbox
By Matt Scales and Jeff Posnick

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express-style routes
It helps with SEO too!

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various network strategies
cache first, network first, fastest,
cache only, network only

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“read through cache”
always stay up to date

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Our learnings
‣ cache busting (one version behind)
‣ avoid dynamic content in shells
‣ skipWaiting so that new SW can override existing SW
immediately
‣ 301s are currently dangerous

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Tracking/Analytics

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Our learnings
‣ important for perf consideration
‣ be wary of automatic UI hooks
‣ tracking library file size
‣ queue events before library loads?
‣ CSP can cause havoc with beacons!

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CORS
Cross Origin Resource Sharing

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CORS
‣ api might be on different domain/hostname
‣ especially on dev/staging envs
‣ API server needs to understand OPTIONS request
‣ respond with correct access-control headers
‣ browser plugins for debugging on dev machine

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Splash screen
Two is better than one!

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Performance
‣ treat performance as a feature
‣ RAIL: Response, Animation, Idle, Load
‣ animate the right properties: transform and opacity
‣ DevTools is your friend!
‣ trace on the device

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What’s next?
‣ HTTP2
‣ HTML streaming
‣ link prefetch
‣ script type module