Performance regression when rendering many events on React state change

[ViniciusMargotti]

Reduced Test Case

https://codesandbox.io/p/sandbox/react-fullcalendar-6-0-5tjvyl

Do you understand that if a reduced test case is not provided, we will intentionally delay triaging of your ticket?

• I understand

Which connector are you using (React/Angular/etc)?

No connector (vanilla JS)

Bug Description

Hello, we identified a much lower performance in our project, especially in drag/drop
By upgrading version v4 to version v5 or v6, you can clearly verify that version 4
It has much better performance, is there any solution to this problem?

Below are examples to check the difference in drag performance

V4
https://codesandbox.io/p/sandbox/react-fullcalendar-4-0-forked-6rn639

V5
https://codesandbox.io/p/sandbox/react-fullcalendar-5-0-gnfcs8

V6
https://codesandbox.io/p/sandbox/react-fullcalendar-6-0-5tjvyl

We identified this issue, when upgrading to version 6.X.X to use new features, we need to be able to view at least 2000 records during the week

[acerix]

Thanks for the demos, I can see the lower performance in the newer versions.

It seems the issue is with using React state to update the calendar data, using the calendar API to update the data should avoid that issue. There's a related issue here:
#7488