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A Pinterest Progressive Web App Performance Case Study

Last updated 3 years ago by Addy Osmani


Pinterest’s new mobile web experience is a Progressive Web App. In this post we’ll cover some of their work to load fast on mobile hardware by keeping JavaScript bundles lean and adopting Service Workers for network resilience.

Why a Progressive Web App (PWA)? Some history.

The Pinterest PWA started because they were focused on international growth, which led them to the mobile web.

After analyzing usage for unauthenticated mobile web users, they realized that their old, slow web experience only managed to convert 1% of users into sign-ups, logins or native app installs. The opportunity to improve this conversation rate was huge, leading them to an investment in the PWA.

Building and shipping a PWA in a quarter

Over 3 months, Pinterest rebuilt their mobile web experience using React, Redux and webpack. Their mobile web rewrite led to several positive improvements in core business metrics.

Time spent is up by 40% compared to the old mobile web experience, user-generated ad revenue is up 44% and core engagements are up 60%:

Their mobile web rewrite also led to several improvements in performance.

Loading fast on average mobile hardware over 3G

Pinterest’s old mobile web experience was a monolith — it included large bundles of CPU-heavy JavaScript that pushed out how quickly Pin pages could load and get interactive.

Users often had to wait 23 seconds before any UI was usable at all:

Pinterest’s old mobile web site took 23 seconds to get interactive. They would send down over 2.5MB of JavaScript (~1.5MB for the main bundle, 1MB lazily loaded in) taking multiple seconds to get parsed and compiled before the main thread finally settled down enough to be interactive.

Their new mobile web experience is a drastic improvement.

Not only did they break-up & shave hundreds of KB off their JavaScript, taking down the size of their core bundle from 650KB to 150KB but they also improved on key performance metrics. First Meaningful Paint was down from 4.2s to 1.8s and Time To Interactive reduced from 23s to 5.6s.

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