By Addy Osmani CHAPTER 6

Chapter siX · by addy Osmani

finDing anD fiXing

Mobile web RenDeRing iSSueS

he performance conversation is starting to change.
It’s no longer important just to consider how quickly a site loads
but also how fast it renders and runs — this is critical on mobile
where the performance of Web pages is often compared to native appli-
cations. Browsers today are able to run at the refresh rate of our devices
and when they do, our pages feel a lot smoother. They’re buttery, crisp and
delightful to use. When they don’t, and users see visual glitches in their
pages, they don’t like that. There’s a performance smell of something being
wrong with the page and it’s something we need to fix.
This can be a challenge as mobile devices are underpowered when
compared to our desktop systems. Rendering the page on the screen takes
longer; loading network resources takes longer; decoding images takes lon-
ger; and executing scripts takes longer. Performance on mobile is almost
never equal to performance on desktop. With slower CPUs and lower-pow-
ered GPUs, mobile platforms are anywhere up to five times slower than
desktop today^1. That said, graphics and mobile JavaScript have been getting
better on such devices and 30 frames per second (fps) is said to be achiev-
able for a number of use cases.

1 http://www.sencha.com/blog/5-myths-about-mobile-web-performance/

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