diff --git a/website/docs/docusaurus-core.mdx b/website/docs/docusaurus-core.mdx index 7e6615d884..e18459b18d 100644 --- a/website/docs/docusaurus-core.mdx +++ b/website/docs/docusaurus-core.mdx @@ -433,6 +433,64 @@ const MyComponent = () => { }; ``` +#### A caveat to know when using `useIsBrowser` + +Because it does not do `typeof windows !== 'undefined'` check but rather checks if the React app has successfully hydrated, the following code will not work as intended: + +```jsx +import React from 'react'; +import useIsBrowser from '@docusaurus/useIsBrowser'; + +const MyComponent = () => { + // highlight-start + const isBrowser = useIsBrowser(); + const url = isBrowser ? new URL(window.location.href) : undefined; + const someQueryParam = url?.searchParams.get('someParam'); + const [someParam, setSomeParam] = useState(someQueryParam || 'fallbackValue'); + + // renders fallbackValue instead of the value of someParam query parameter + // because the component has already rendered but hydration has not completed + // useState references the fallbackValue + return {someParam}; + // highlight-end +}; +``` + +Adding `useIsBrowser()` checks to derived values will have no effect. Wrapping the `` with `` will also have no effect. To have `useState` reference the correct value, which is the value of the `someParam` query parameter, `MyComponent`'s first render should actually happen after `useIsBrowser` returns true. Because you cannot have if statements inside the component before any hooks, you need to resort to doing `useIsBrowser()` in the parent component as such: + +```jsx +import React, {useState} from 'react'; +import useIsBrowser from '@docusaurus/useIsBrowser'; + +const MyComponent = () => { + const isBrowser = useIsBrowser(); + const url = isBrowser ? new URL(window.location.href) : undefined; + const someQueryParam = url?.searchParams.get('someParam'); + const [someParam, setSomeParam] = useState(someQueryParam || 'fallbackValue'); + + return {someParam}; +}; + +// highlight-start +const MyComponentParent = () => { + const isBrowser = useIsBrowser(); + + if (!isBrowser) { + return null; + } + + return ; +}; +// highlight-end + +export default MyComponentParent; +``` + +There are a couple more alternative solutions to this problem. However all of them require adding checks in **the parent component**: + +1. You can wrap `` with [`BrowserOnly`](../docusaurus-core.mdx#browseronly) +2. You can use `canUseDOM` from [`ExecutionEnvironment`](../docusaurus-core.mdx#executionenvironment) and `return null` when `canUseDOM` is `false` + ### `useBaseUrl` {#useBaseUrl} React hook to prepend your site `baseUrl` to a string.