reactjs / reactjs/react.dev

[Suggestion]: StrictMode confusion about ordering of the events

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还没有人认领这个 Issue。

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描述

Summary

This thread comes really close to avoid repeating this question again.
However I still have some doubts about the chain of the events in the strict mode.

I will quote the answer which provide the most valuable feedback.

"The mental model for this is that React really does unmount the component, but when re-mounting the component we restore the previously used state instead of starting fresh, the way Fast Refresh does, or some future features will."

But if that's the case why the order of the events(rendering, setting state, effects etc) is different while running in strict mode and outside of it?

Here are the concrete examples:

  1. https://codesandbox.io/p/sandbox/2z4wq2. This sandbox runs inside a strict mode and by inspecting the console we can see that the order of the events is like this
render
state setter
render
state setter
effect
clean up
effect

The second render and state setter are dimmed out according to the documentation and that's fine. So at least on the surface it appears that react is triggering render function (and state setter) 2 times before moving to the effects.

  1. https://codesandbox.io/p/sandbox/93zfkw. This sandbox runs outside of the strict mode and there is a button to toggle the mounting of the component. If the component is mounted, unmounted and mounted again the order of the events is like this.
render
state setter
effect
clean up
render
state setter
effect

This example has the mental model I have always worked with and which is clear, so I would waste too much time on it since that's how React also behaves on production.

The question is, if react is really performing mounting, unmounting and remounting while is the order different?

To be honest I haven't noticed that this difference is making my code harder to reason about while working with StrictMode.
I would like to know the details, if possible. What does this approach help React achieve that original one does not?

Page

https://react.dev/reference/react/StrictMode

Details

I think it would be helpful to update the page to explain why the behavior in StrictMode is different than simply running mounting, unmounting and mounting again.

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  3. Fork 仓库,在一个分支上完成修改。
  4. 提交 Pull Request,并在描述里引用这个 Issue 编号。

调研方向

从 React StrictMode 参考页面开始,将其当前的说明与链接的 issue 讨论串和两个 CodeSandbox 示例进行比较。阐明 StrictMode 中观察到的 render、state、effect 和 cleanup 顺序为何不同于单独的 mount-unmount-remount 周期,并更新页面,使说明能够回答这一差异。

由索引模型根据 Issue 内容生成。

评估

技术栈
javascript, react
领域
documentation
Issue 类型
文档
难度
4/5
预计耗时
3-5 天
活跃度
停滞
描述清晰度
基本清楚
新手友好度
35/100

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