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Server side render everything amazon.com is server side rendered and has no client side rendering framework. The potential latency hit didn't justify it. We were stuck with jQuery 1.6.4

SSR React wasn't fast enough for us. This blew my mind.

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Track critical performance metrics We tracked: • time to load content above the fold • time to first suggestion • time to visual completeness • time to load ads • time to page layout ready • and many more...

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A/B test all critical changes If any release regressed our sales metrics, we'd revert. Simple as that.

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Drop unused polyfills Amazon still supports IE 10, which doesn't support Promises. We polyfilled it on IE but dropped it for modern browsers. I led the work for this! We dropped critical JS bundles by 10kb.

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Serve browser-specific bundles We detected browsers server side (via UA sniffing) and served bundles optimized for that browser. Teams could optionally define browser-specific features via a module's filename (ex. ./my-feature.ie.js)

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Love web performance? Follow me,

and

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Btw I'm building

to make the web 10x faster! Follow for all things web perf

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Replying to

Great thread

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What does “fold” mean? First time I’ve heard that as a term.

Jan 23

Good question, hope this clarifies

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I couldn't find a lot of modern articles about ATF, seems to be a less popular optimization those days. Any recommended articles? I don't understand how you can know ahead of time what is above the fold and what isn't unless you're using hight 100vh in your css.

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Very cool. Is this basically loading all content that’s viewable first before rendering the rest of the page?

Yup!

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Insightful thread, thanks. Just curious, how did you know the 5% increase was due to the ATF change and not, say seasonal fluctuations/a marketing push/etc?

Andrew Guenther

@codebrewed

Jan 24

A/B testing. 50% of users get one version, 50% another. Compare sales for both groups.

Replying to

Amazon has been doing above the fold content loading for almost a decade, this isn't new.