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スウィズリング（Swizzling）

ここでは、Docusaurusでレイアウトをカスタマイズする方法を紹介します。

見覚えがあるような……？

This section is similar to Styling and Layout, but this time, we will customize React components themselves, rather than what they look like. We will talk about a central concept in Docusaurus: swizzling, which allows deeper site customizations.

In practice, swizzling permits to swap a theme component with your own implementation, and it comes in 2 patterns:

  • Ejecting: creates a copy of the original theme component, which you can fully customize
  • Wrapping: creates a wrapper around the original theme component, which you can enhance
Why is it called swizzling?

The name comes from Objective-C and Swift-UI: method swizzling is the process of changing the implementation of an existing selector (method).

For Docusaurus, component swizzling means providing an alternative component that takes precedence over the component provided by the theme.

You can think of it as Monkey Patching for React components, enabling you to override the default implementation. Gatsby has a similar concept called theme shadowing.

To gain a deeper understanding of this, you have to understand how theme components are resolved.

スウィズリングの過程​

概要​

Docusaurus provides a convenient interactive CLI to swizzle components. 通常は、次のコマンドだけ覚えておけば十分です。

npm run swizzle

It will generate a new component in your src/theme directory, which should look like this example:

src/theme/SomeComponent.js
import React from 'react';

export default function SomeComponent(props) {
  // You can fully customize this implementation
  // including changing the JSX, CSS and React hooks
  return (
    <div className="some-class">
      <h1>Some Component</h1>
      <p>Some component implementation details</p>
    </div>
  );
}

スウィズリング可能な全てのテーマとコンポーネントの概要を把握するには、次のコマンドを実行してください。

npm run swizzle -- --list

Use --help to see all available CLI options, or refer to the reference swizzle CLI documentation.

Removing Unneeded Swizzled Components

過去にスウィズリングしたコンポーネントが不要になった場合は、それらのファイルを src/theme ディレクトリから簡単に削除できます。 After removing the component, make sure to restart your development server to ensure the changes are properly reflected.

メモ

After swizzling a component, restart your dev server in order for Docusaurus to know about the new component.

Prefer staying on the safe side

Be sure to understand which components are safe to swizzle. Some components are internal implementation details of a theme.

情報

docusaurus swizzle is only an automated way to help you swizzle the component. You can also create the src/theme/SomeComponent.js file manually, and Docusaurus will resolve it. このコマンドの中に魔法などありません！

取り出し（Ejecting）​

Ejecting a theme component is the process of creating a copy of the original theme component, which you can fully customize and override.

To eject a theme component, use the swizzle CLI interactively, or with the --eject option:

npm run swizzle [テーマ名] [コンポーネント名] -- --eject

例：

npm run swizzle @docusaurus/theme-classic Footer -- --eject

This will copy the current <Footer /> component's implementation to your site's src/theme directory. Docusaurus will now use this <Footer> component copy instead of the original one. You are now free to completely re-implement the <Footer> component.

src/theme/Footer/index.js
import React from 'react';

export default function Footer(props) {
  return (
    <footer>
      <h1>This is my custom site footer</h1>
      <p>And it is very different from the original</p>
    </footer>
  );
}
警告

Ejecting an unsafe component can sometimes lead to copying a large amount of internal code, which you now have to maintain yourself. 受け取ったプロパティや使用する内部テーマAPIが変更された場合、カスタマイズした内容を移行する必要があるため、Docusaurusのアップグレードをより困難にすることがあります。

Prefer wrapping whenever possible: the amount of code to maintain is smaller.

Re-swizzling

To keep ejected components up-to-date after a Docusaurus upgrade, re-run the eject command and compare the changes with git diff. また、ファイルの最初に、行った変更点の簡単な説明を書くことをお勧めします。これにより、再取り出し後にあなたの変更を簡単に再適用できるでしょう。

ラッピング（Wrapping）​

Wrapping a theme component is the process of creating a wrapper around the original theme component, which you can enhance.

To wrap a theme component, use the swizzle CLI interactively, or with the --wrap option:

npm run swizzle [テーマ名] [コンポーネント名] -- --wrap

例：

npm run swizzle @docusaurus/theme-classic Footer -- --wrap

This will create a wrapper in your site's src/theme directory. Docusaurus will now use the <FooterWrapper> component instead of the original one. これで、元のコンポーネントの周りにカスタマイズを加えることができます。

src/theme/Footer/index.js
import React from 'react';
import Footer from '@theme-original/Footer';

export default function FooterWrapper(props) {
  return (
    <>
      <section>
        <h2>Extra section</h2>
        <p>This is an extra section that appears above the original footer</p>
      </section>
      <Footer {...props} />
    </>
  );
}
What is this @theme-original thing?

Docusaurus uses theme aliases to resolve the theme components to use. The newly created wrapper takes the @theme/SomeComponent alias. @theme-original/SomeComponent permits to import original component that the wrapper shadows without creating an infinite import loop where the wrapper imports itself.

ヒント

Wrapping a theme is a great way to add extra components around existing one without ejecting it. For example, you can easily add a custom comment system under each blog post:

src/theme/BlogPostItem.js
import React from 'react';
import BlogPostItem from '@theme-original/BlogPostItem';
import MyCustomCommentSystem from '@site/src/MyCustomCommentSystem';

export default function BlogPostItemWrapper(props) {
  return (
    <>
      <BlogPostItem {...props} />
      <MyCustomCommentSystem />
    </>
  );
}

スウィズリングしても安全なもの ​

大いなる力には、大いなる責任を伴う

Some theme components are internal implementation details of a theme. Docusaurus allows you to swizzle them, but it might be risky.

Why is it risky?

Theme authors (including us) might have to update their theme over time: changing the component props, name, file system location, types... For example, consider a component that receives two props name and age, but after a refactor, it now receives a person prop with the above two properties. Your component, which still expects these two props, will render undefined instead.

Moreover, internal components may simply disappear. If a component is called Sidebar and it's later renamed to DocSidebar, your swizzled component will be completely ignored.

Theme components marked as unsafe may change in a backward-incompatible way between theme minor versions. When upgrading a theme (or Docusaurus), your customizations might behave unexpectedly, and can even break your site.

For each theme component, the swizzle CLI will indicate 3 different levels of safety declared by theme authors:

  • Safe: this component is safe to be swizzled, its public API is considered stable, and no breaking changes should happen within a theme major version
  • Unsafe: this component is a theme implementation detail, not safe to be swizzled, and breaking changes might happen within a theme minor version
  • Forbidden: the swizzle CLI will prevent you from swizzling this component, because it is not designed to be swizzled at all
メモ

Some components might be safe to wrap, but not safe to eject.

情報

Don't be too afraid to swizzle unsafe components: just keep in mind that breaking changes might happen, and you might need to upgrade your customizations manually on minor version upgrades.

Report your use-case

If you have a strong use-case for swizzling an unsafe component, please report it here and we will work together to find a solution to make it safe.

どのコンポーネントをスウィズリングすべきか ​

It is not always clear which component you should swizzle exactly to achieve the desired result. @docusaurus/theme-classic, which provides most of the theme components, has about 100 components!

ヒント

To print an overview of all the @docusaurus/theme-classic components:

npm run swizzle @docusaurus/theme-classic -- --list

You can follow these steps to locate the appropriate component to swizzle:

  1. Component description. Some components provide a short description, which is a good way to find the right one.
  2. Component name. Official theme components are semantically named, so you should be able to infer its function from the name. The swizzle CLI allows you to enter part of a component name to narrow down the available choices. For example, if you run yarn swizzle @docusaurus/theme-classic, and enter Doc, only the docs-related components will be listed.
  3. Start with a higher-level component. Components form a tree with some components importing others. Every route will be associated with one top-level component that the route will render (most of them listed in Routing in content plugins). For example, all blog post pages have @theme/BlogPostPage as the topmost component. You can start with swizzling this component, and then go down the component tree to locate the component that renders just what you are targeting. Don't forget to unswizzle the rest by deleting the files after you've found the correct one, so you don't maintain too many components.
  4. Read the theme source code and use search wisely.
Just ask!

If you still have no idea which component to swizzle to achieve the desired effect, you can reach out for help in one of our support channels.

We also want to understand better your fanciest customization use-cases, so please report them.

スウィズリングを行う必要があるか ​

Swizzling ultimately means you have to maintain some additional React code that interact with Docusaurus internal APIs. If you can, think about the following alternatives when customizing your site:

  1. Use CSS. CSS rules and selectors can often help you achieve a decent degree of customization. Refer to styling and layout for more details.
  2. Use translations. It may sound surprising, but translations are ultimately just a way to customize the text labels. For example, if your site's default language is en, you can still run yarn write-translations -l en and edit the code.json emitted. Refer to the i18n tutorial for more details.
ヒント

The smaller, the better. If swizzling is inevitable, prefer to swizzle only the relevant part and maintain as little code on your own as possible. Swizzling a small component often means less risk of breaking changes during upgrade.

Wrapping is also a far safer alternative to ejecting.

Wrapping your site with <Root>​

The <Root> component is rendered at the very top of the React tree, above the theme <Layout>, and never unmounts. It is the perfect place to add stateful logic that should not be re-initialized across navigations (user authentication status, shopping cart state...).

Swizzle it manually by creating a file at src/theme/Root.js:

src/theme/Root.js
import React from 'react';

// Default implementation, that you can customize
export default function Root({children}) {
  return <>{children}</>;
}
ヒント

React Contextプロバイダをレンダリングするには、このコンポーネントを使用してください。