Refine "Separating Events from Effects"

[smikitky]

こういうこと言われており、読み返してみたら指摘もさもありなんという感じだったので、改善したものです。

[github-actions[bot]]

Size changes

## 📦 Next.js Bundle Analysis for react-dev This analysis was generated by the [Next.js Bundle Analysis action](https://github.com/hashicorp/nextjs-bundle-analysis). 🤖 ### Three Pages Changed Size The following pages changed size from the code in this PR compared to its base branch: Page | Size (compressed) | First Load | |---|---|---| | `/404` | `79.65 KB` _(-5 B)_ | 183.48 KB | | `/500` | `79.64 KB` _(-5 B)_ | 183.48 KB | | `/[[...markdownPath]]` | `81.5 KB` _(-5 B)_ | 185.33 KB |

Details

Only the gzipped size is provided here based on an expert tip.

First Load is the size of the global bundle plus the bundle for the individual page. If a user were to show up to your website and land on a given page, the first load size represents the amount of javascript that user would need to download. If next/link is used, subsequent page loads would only need to download that page's bundle (the number in the "Size" column), since the global bundle has already been downloaded.

Any third party scripts you have added directly to your app using the <script> tag are not accounted for in this analysis

Next to the size is how much the size has increased or decreased compared with the base branch of this PR. If this percentage has increased by 10% or more, there will be a red status indicator applied, indicating that special attention should be given to this.