NEW 272889
CSS Highlights API poor performance compared to Chrome 
https://bugs.webkit.org/show_bug.cgi?id=272889
Summary CSS Highlights API poor performance compared to Chrome
Keith Cirkel
Reported 2024-04-18 03:51:16 PDT
Steps to reproduce: 1. Visit https://codepen.io/bramus/pen/MWxLjEo 2. Visit https://code.jquery.com/jquery-3.7.1.js and copy the contents 3. Paste the contents into the codepen demo textarea 4. Try scrolling around 5. Observe the stark performance difference between Safari & Chrome
Attachments
Web Inspector Timeline (191.10 KB, image/png)
2024-04-19 02:36 PDT, Karl Dubost 		no flags
Details
View All Add attachment proposed patch, testcase, etc.
Anthony Ricaud
Comment 1 2024-04-18 04:40:03 PDT
ccing Megan for awareness as she was involved in the implementation
Radar WebKit Bug Importer
Comment 2 2024-04-19 02:26:25 PDT
<rdar://problem/126741543>
Karl Dubost
Comment 3 2024-04-19 02:29:59 PDT
It takes a long time to highlight everything. Once all the code is highlighted the scrolling is working fine.
Karl Dubost
Comment 4 2024-04-19 02:36:57 PDT
Created attachment 471004 [details] Web Inspector Timeline it takes on my machine ~120s before being fully highlighted, with the CPU maxing out. On the JS side it doesn't do much it seems.
Anthony Ricaud
Comment 5 2024-04-19 04:01:23 PDT
> Once all the code is highlighted the scrolling is working fine. I notice a big difference in scrolling behaviour: With the focus outside the contenteditable area, going from the top to the bottom of the page (or vice versa, with Home/End keys) is pretty quick but with a flash of white screen. With the focus inside the contenteditable area, the same action takes tens of seconds.
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