Mastodawn

requestIdleCallback has been available in all browsers for yeaars
except~
Safari

WebKit delayed shipping this somewhat on purpose.

They found repeatedly that enabling it made performance worse, because the typical fallback is setTimeout, and that pushes things further back than rIC. And because people often overuse rIC, letting code take the other path can lead to better page load times / better resource utilisation.

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Timo Tijhof

@nullvoxpopuli

WebKit landed rIC years ago, but kept reverting the feature flag toggle due to regressing page load time on real-world sites like Wikipedia and Google Search.

Delaying JS code, even at random, often make sites perform better :-)

(Wikipedia uses rIC in MediaWiki's ResourceLoader to async eval from localStorage and when unpacking a large module bundles.)

Rabbit hole starts at:

https://github.com/search?q=repo%3AWebKit%2FWebKit+requestIdleCallback+&type=commits&s=committer-date&o=asc

https://bugs.webkit.org/show_bug.cgi?id=285049

https://www.mediawiki.org/wiki/ResourceLoader/Architecture

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#webkit #webperf

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