On devices without a top-notch CPU, typing in the rich text editor is
laggy even in the very basic community test suite's "Post" collection.
Lags can be up to multiple seconds. This lag can be reproduced by e.g.
throttling the CPU by 6x on a MacBook Pro with M1 Pro chip and 32GB of
RAM. Typing at regular speed already stutters, and the Chromium
performance monitor shows 100% peak CPU utilization. Under the same
circumstances, the Lexical rich text editor on
https://playground.lexical.dev/ does not exhibit the same laggy UI
reactions.
The issue was narrowed down to the editor state serialization that was
so far executed on every change in `Field.tsx` and utilizing more than 1
frame's worth of CPU time.
This PR attempts to address the issue by asking the browser to queue the
work in moments where it doesn't interfere with UI responsiveness, via
`requestIdleCallback`.
To verify this change, simulate a slow CPU by setting `CPU: 6x slowdown`
in the Chromium `Performance` Dev Tool panel, and then type into the
community test suite's example post's rich text field.
I did not collect exhaustive benchmarks, since numbers are system
specific and the impact of the code change is simple to verify.
Demos:
Before, whole words are not appearing while typing, but then appear all
at once, INP is 6s, and CPU at 100% basically the whole interaction
time:
https://github.com/user-attachments/assets/535653d5-c9e6-4189-a0e0-f71d39c43c31
After: Most letters appear without delay, individual letters can be
slightly delayed, but INP is much more reasonable 350ms, and CPU has
enough bandwidth to drop below 100% utilization:
https://github.com/user-attachments/assets/e627bf50-b441-41de-b3a3-7ba5443ff049⬆️ This recording is from an earlier solution attempt with 500ms
debouncing. The current approach with `requestIdleCallback` increases
CPU usage back to a close 100%, but the INP is further reduced to 2xxms
on my machine, and the perceived UI laggyness is comparable to this
recording.
---
This PR only addresses the rich text editor, because that's where the
performance was a severe usability deal-breaker for real world usage.
Presumably other input fields where users trigger a lot of change events
in succession such as text, textarea, number, and JSON fields might also
benefit from similar debouncing.
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