Bug 232673

Summary: CSS outlines in contenteditable elements causes performance issues
Product: WebKit Reporter: Brian Kim <briankimpossible>
Component: HTML EditingAssignee: Nobody <webkit-unassigned>
Status: NEW ---    
Severity: Normal CC: briankimpossible, loginwebkit, megan_gardner, simon.fraser, webkit-bug-importer, wenson_hsieh, zalan
Priority: P2 Keywords: InRadar
Version: Safari 15   
Hardware: Mac (Apple Silicon)   
OS: macOS 11   
Attachments:
Description Flags
Safari Devtools timeline dump none

Description Brian Kim 2021-11-03 11:15:45 PDT 
Created attachment 443215 [details]
Safari Devtools timeline dump

Typing in contenteditable elements is slow when using the default focused outline CSS rules.

Steps to reproduce:
1. Go to https://www.slatejs.org/examples/plaintext
2. Inspect the contenteditable element and disable the `outline: none` style.
3. Try inserting many newlines using the Enter key.
4. When there is a visible outline, you should see noticeable lag and frame drops as the document size increases.
5. This lag does not exist when the `outline: none` style is re-enabled.

I’ve attached a timeline export from Safari Devtools. The important detail is that in the frames view, Devtools reports that time is spent in Other (not Layout, Painting, Scripting). I do not have the ability to investigate further at this time.
Comment 1 Radar WebKit Bug Importer 2021-11-10 10:16:35 PST 
<rdar://problem/85259554>