---
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
### `
`
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 {2,6,11}
import React from 'react';
import Head from '@docusaurus/Head';
const MySEO = () => (
<>
);
```
Nested or latter components will override duplicate usages:
```jsx {2,5,8,11}
My TitleNested Title
```
Outputs
```html
```
### ``
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 `` 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-router’s `` component that adds useful enhancements specific to Docusaurus. All props are passed through to react-router’s `` component.
```jsx {2,7}
import React from 'react';
import Link from '@docusaurus/Link';
const Page = () => (
Check out my blog!
{/* Note that external links still use `a` tags, but automatically opens in new tab. */}
Follow me on Twitter!
);
```
#### `to`: string
The target location to navigate to. Example: `/docs/introduction`.
```jsx
```
### ``
Rendering a `` 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';
function Home() {
return ;
}
```
:::note
`@docusaurus/router` implements [React Router](https://reacttraining.com/react-router/web/guides/quick-start) and supports its features.
:::
### ``
The `` 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
import BrowserOnly from '@docusaurus/BrowserOnly';
function MyComponent() {
return (
The fallback content to display on prerendering}>
{() => {
// Something that should be excluded during build process prerendering.
}}
);
}
```
## Hooks
### `useDocusaurusContext`
React hook to access Docusaurus Context. Context contains `siteConfig` object from [docusaurus.config.js](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;
}
interface DocusaurusContext {
siteConfig: DocusaurusConfig;
siteMetadata: DocusaurusSiteMetadata;
}
```
Usage example:
```jsx {5,8,9}
import React from 'react';
import useDocusaurusContext from '@docusaurus/useDocusaurusContext';
const MyComponent = () => {
const {siteConfig, siteMetadata} = useDocusaurusContext();
return (
{siteConfig.title}
{siteMetadata.siteVersion}
{siteMetadata.docusaurusVersion}
);
};
```
### `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';
function Help() {
return (
Browse the docs
Learn more about Docusaurus using the{' '}
official documentation
);
}
```
### `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 {2,5,6,7}
import React from 'react';
import {useBaseUrlUtils} from '@docusaurus/useBaseUrl';
function Component() {
const urls = ['/a', '/b'];
const {withBaseUrl} = useBaseUrlUtils();
const urlsWithBaseUrl = urls.map(withBaseUrl);
return
{/* ... */}
;
}
```
## 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}
import React from 'react';
import ExecutionEnvironment from '@docusaurus/ExecutionEnvironment';
function MyPage() {
const location = ExecutionEnvironment.canUseDOM ? window.location.href : null;
return
{location}
;
}
```
| 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`. |