docusaurus/website/docs/docusaurus-core.md
Sébastien Lorber a8ee7fd3e8
docs(v2): i18n doc + polish (#4014)
* add some initial i18n doc

* i18n doc progress

* i18n tutorial progress

* i18n tutorial progress

* polish Crowdin docs

* i18n sidebar in guides

* polish crowdin doc

* update Crowdin doc a bit

* fix annoying relative link to global site resource in template (breaks i18n tutorial)

* template: use simpler export for homepage

* add markdown page example

* rename mdx.md to interactiveDoc.mdx

* update bootstrap/facebook templates too

* sync init template package scripts

* add slug frontmatter doc

* improve i18n doc

* complete i18n doc

* temporarily enable the localeDropdown

* doc typo

* improve the i18n doc

* Add Git i18n doc

* add missing "--" for npm run options (unfortunately they don't get stripped by npm2yarn, and are required foor npm)

* improve a bit the Crowdin doc
2021-01-19 17:26:31 +01:00

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---
id: docusaurus-core
title: Docusaurus Client API
sidebar_label: Client API
---
Docusaurus provides some APIs on the clients that can be helpful to you when building your site.
## Components
### `<Head/>`
This reusable React component will manage all of your changes to the document head. It takes plain HTML tags and outputs plain HTML tags and is beginner-friendly. It is a wrapper around [React Helmet](https://github.com/nfl/react-helmet).
Usage Example:
```jsx {2,5,10}
import React from 'react';
import Head from '@docusaurus/Head';
const MySEO = () => (
<Head>
<meta property="og:description" content="My custom description" />
<meta charSet="utf-8" />
<title>My Title</title>
<link rel="canonical" href="http://mysite.com/example" />
</Head>
);
```
Nested or latter components will override duplicate usages:
```jsx {2,5,8,11}
<Parent>
<Head>
<title>My Title</title>
<meta name="description" content="Helmet application" />
</Head>
<Child>
<Head>
<title>Nested Title</title>
<meta name="description" content="Nested component" />
</Head>
</Child>
</Parent>
```
Outputs:
```html
<head>
<title>Nested Title</title>
<meta name="description" content="Nested component" />
</head>
```
### `<Link/>`
This component enables linking to internal pages as well as a powerful performance feature called preloading. Preloading is used to prefetch resources so that the resources are fetched by the time the user navigates with this component. We use an `IntersectionObserver` to fetch a low-priority request when the `<Link>` is in the viewport and then use an `onMouseOver` event to trigger a high-priority request when it is likely that a user will navigate to the requested resource.
The component is a wrapper around react-routers `<Link>` component that adds useful enhancements specific to Docusaurus. All props are passed through to react-routers `<Link>` component.
```jsx {2,7}
import React from 'react';
import Link from '@docusaurus/Link';
const Page = () => (
<div>
<p>
Check out my <Link to="/blog">blog</Link>!
</p>
<p>
{/* Note that external links still use `a` tags, but automatically opens in new tab. */}
Follow me on <a href="https://twitter.com/docusaurus">Twitter</a>!
</p>
</div>
);
```
#### `to`: string
The target location to navigate to. Example: `/docs/introduction`.
```jsx
<Link to="/courses" />
```
### `<Redirect/>`
Rendering a `<Redirect>` will navigate to a new location. The new location will override the current location in the history stack, like server-side redirects (HTTP 3xx) do. You can refer to [React Router's Redirect documentation](https://reacttraining.com/react-router/web/api/Redirect) for more info on available props.
Example usage:
```jsx {2,5}
import React from 'react';
import {Redirect} from '@docusaurus/router';
const Home = () => {
return <Redirect to="/docs/test" />;
};
```
:::note
`@docusaurus/router` implements [React Router](https://reacttraining.com/react-router/web/guides/quick-start) and supports its features.
:::
### `<BrowserOnly/>`
The `<BrowserOnly>` component accepts a `children` prop, a render function which will not be executed during the pre-rendering phase of the build process. This is useful for hiding code that is only meant to run in the browsers (e.g. where the `window`/`document` objects are being accessed). To improve SEO, you can also provide fallback content using the `fallback` prop, which will be prerendered until in the build process and replaced with the client-side only contents when viewed in the browser.
```jsx {1,5-10}
import BrowserOnly from '@docusaurus/BrowserOnly';
const MyComponent = () => {
return (
<BrowserOnly
fallback={<div>The fallback content to display on prerendering</div>}>
{() => {
// Something that should be excluded during build process prerendering.
}}
</BrowserOnly>
);
};
```
### `<Translate/>`
When [localizing your site](./i18n/i18n-introduction.md), the `<Translate/>` component will allow providing **translation support to React components**, such as your homepage.
The translation strings will be extracted from your code with the [`docusaurus write-translations`](./cli.md#docusaurus-write-translations) CLI and create a `code.json` translation file in `website/i18n/<locale>`.
:::note
The `<Translate/>` props **must be hardcoded strings**.
It is **not possible to use variables**, or the extraction wouldn't work.
:::
#### Props
- `children`: untranslated string in the default site locale`
- `id`: optional value to use as key in JSON translation files
- `description`: optional text to help the translator
#### Example
```jsx title="src/index.js"
import React from 'react';
import Layout from '@theme/Layout';
// highlight-start
import Translate from '@docusaurus/Translate';
// highlight-end
export default function Home() {
return (
<Layout>
<h1>
{/* highlight-start */}
<Translate
id="homepage.title"
description="The homepage welcome message">
Welcome to my website
</Translate>
{/* highlight-end */}
</h1>
<main>
{/* highlight-start */}
<Translate>My website content</Translate>
{/* highlight-end */}
</main>
</Layout>
);
}
```
## Hooks
### `useDocusaurusContext`
React hook to access Docusaurus Context. Context contains `siteConfig` object from [docusaurus.config.js](api/docusaurus.config.js.md), and some additional site metadata.
```ts
type DocusaurusPluginVersionInformation =
| {readonly type: 'package'; readonly version?: string}
| {readonly type: 'project'}
| {readonly type: 'local'}
| {readonly type: 'synthetic'};
interface DocusaurusSiteMetadata {
readonly docusaurusVersion: string;
readonly siteVersion?: string;
readonly pluginVersions: Record<string, DocusaurusPluginVersionInformation>;
}
interface DocusaurusContext {
siteConfig: DocusaurusConfig;
siteMetadata: DocusaurusSiteMetadata;
}
```
Usage example:
```jsx {5,8-10}
import React from 'react';
import useDocusaurusContext from '@docusaurus/useDocusaurusContext';
const MyComponent = () => {
const {siteConfig, siteMetadata} = useDocusaurusContext();
return (
<div>
<h1>{siteConfig.title}</h1>
<div>{siteMetadata.siteVersion}</div>
<div>{siteMetadata.docusaurusVersion}</div>
</div>
);
};
```
### `useBaseUrl`
React hook to automatically prepend `baseUrl` to a string automatically. This is particularly useful if you don't want to hardcode your config's `baseUrl`. We highly recommend you to use this.
```ts
type BaseUrlOptions = {
forcePrependBaseUrl: boolean;
absolute: boolean;
};
```
Example usage:
```jsx {3,11}
import React from 'react';
import Link from '@docusaurus/Link';
import useBaseUrl from '@docusaurus/useBaseUrl';
const Help = () => {
return (
<div className="col">
<h2>Browse the docs</h2>
<p>
Learn more about Docusaurus using the{' '}
<Link to={useBaseUrl('docs/introduction')}>official documentation</Link>
</p>
</div>
);
};
```
### `useBaseUrlUtils`
Sometimes `useBaseUrl` is not good enough. This hook return additional utils related to your site's base url.
- `withBaseUrl`: useful if you need to add base urls to multiple urls at once
```jsx {2,5-7}
import React from 'react';
import {useBaseUrlUtils} from '@docusaurus/useBaseUrl';
const Component = () => {
const urls = ['/a', '/b'];
const {withBaseUrl} = useBaseUrlUtils();
const urlsWithBaseUrl = urls.map(withBaseUrl);
return <div className="col">{/* ... */}</div>;
};
```
### `useGlobalData`
React hook to access Docusaurus global data created by all the plugins.
Global data is namespaced by plugin name, and plugin id.
:::info
Plugin id is only useful when a plugin is used multiple times on the same site. Each plugin instance is able to create its own global data.
:::
```ts
type GlobalData = Record<
PluginName,
Record<
PluginId, // "default" by default
any // plugin-specific data
>
>;
```
Usage example:
```jsx {2,5-7}
import React from 'react';
import useGlobalData from '@docusaurus/useGlobalData';
const MyComponent = () => {
const globalData = useGlobalData();
const myPluginData = globalData['my-plugin']['default'];
return <div>{myPluginData.someAttribute}</div>;
};
```
:::tip
Inspect your site's global data at `./docusaurus/globalData.json`
:::
### `usePluginData`
Access global data created by a specific plugin instance.
This is the most convenient hook to access plugin global data, and should be used most of the time.
`pluginId` is optional if you don't use multi-instance plugins.
```ts
usePluginData(pluginName: string, pluginId?: string)
```
Usage example:
```jsx {2,5-6}
import React from 'react';
import {usePluginData} from '@docusaurus/useGlobalData';
const MyComponent = () => {
const myPluginData = usePluginData('my-plugin');
return <div>{myPluginData.someAttribute}</div>;
};
```
### `useAllPluginInstancesData`
Access global data created by a specific plugin. Given a plugin name, it returns the data of all the plugins instances of that name, by plugin id.
```ts
useAllPluginInstancesData(pluginName: string)
```
Usage example:
```jsx {2,5-7}
import React from 'react';
import {useAllPluginInstancesData} from '@docusaurus/useGlobalData';
const MyComponent = () => {
const allPluginInstancesData = useAllPluginInstancesData('my-plugin');
const myPluginData = allPluginInstancesData['default'];
return <div>{myPluginData.someAttribute}</div>;
};
```
## Functions
### `translate`
The imperative counterpart of the [`<Translate>`](#translate) component.
:::tip
Use the imperative API for the **rare cases** when a **component cannot be used**, such as:
- the `placeholder` props of form input
- the page `title` metadata
:::
```jsx title="src/index.js"
import React from 'react';
import Layout from '@theme/Layout';
// highlight-start
import {translate} from '@docusaurus/Translate';
// highlight-end
export default function Home() {
return (
<Layout
// highlight-start
title={translate({message: 'My page meta title'})}
// highlight-end
>
<input
type="text"
placeholder={
// highlight-start
translate({
message: 'Some input placeholder',
// Optional
id: 'homepage.input.placeholder',
description: 'The homepage input placeholder',
})
// highlight-end
}
/>
</Layout>
);
}
```
## Modules
### `ExecutionEnvironment`
A module which exposes a few boolean variables to check the current rendering environment. Useful if you want to only run certain code on client/server or need to write server-side rendering compatible code.
```jsx {2,5}
import React from 'react';
import ExecutionEnvironment from '@docusaurus/ExecutionEnvironment';
const MyPage = () => {
const location = ExecutionEnvironment.canUseDOM ? window.location.href : null;
return <div>{location}</div>;
};
```
| Field | Description |
| --- | --- |
| `ExecutionEnvironment.canUseDOM` | `true` if on client, `false` if prerendering. |
| `ExecutionEnvironment.canUseEventListeners` | `true` if on client and has `window.addEventListener`. |
| `ExecutionEnvironment.canUseIntersectionObserver` | `true` if on client and has `IntersectionObserver`. |
| `ExecutionEnvironment.canUseViewport` | `true` if on client and has `window.screen`. |
### `constants`
A module exposing useful constants to client-side theme code.
```jsx
import {DEFAULT_PLUGIN_ID} from '@docusaurus/constants';
```
| Named export | Value |
| ------------------- | --------- |
| `DEFAULT_PLUGIN_ID` | `default` |