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119 lines
3.4 KiB
Markdown
119 lines
3.4 KiB
Markdown
---
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title: "usePreviewMode"
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description: "Use usePreviewMode to check and control preview mode in Nuxt"
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links:
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- label: Source
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icon: i-simple-icons-github
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to: https://github.com/nuxt/nuxt/blob/main/packages/nuxt/src/app/composables/preview.ts
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size: xs
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---
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# `usePreviewMode`
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Preview mode allows you to see how your changes would be displayed on a live site without revealing them to users.
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You can use the built-in `usePreviewMode` composable to access and control preview state in Nuxt. If the composable detects preview mode it will automatically force any updates necessary for [`useAsyncData`](/docs/api/composables/use-async-data) and [`useFetch`](/docs/api/composables/use-fetch) to rerender preview content.
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```js
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const { enabled, state } = usePreviewMode()
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```
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## Options
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### Custom `enable` check
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You can specify a custom way to enable preview mode. By default the `usePreviewMode` composable will enable preview mode if there is a `preview` param in url that is equal to `true` (for example, `http://localhost:3000?preview=true`). You can wrap the `usePreviewMode` into custom composable, to keep options consistent across usages and prevent any errors.
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```js
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export function useMyPreviewMode () {
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return usePreviewMode({
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shouldEnable: () => {
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return !!route.query.customPreview
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}
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});
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}
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```
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### Modify default state
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`usePreviewMode` will try to store the value of a `token` param from url in state. You can modify this state and it will be available for all [`usePreviewMode`](/docs/api/composables/use-preview-mode) calls.
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```js
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const data1 = ref('data1')
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const { enabled, state } = usePreviewMode({
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getState: (currentState) => {
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return { data1, data2: 'data2' }
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}
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})
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```
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::note
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The `getState` function will append returned values to current state, so be careful not to accidentally overwrite important state.
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::
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### Customize the `onEnable` and `onDisable` callbacks
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By default, when `usePreviewMode` is enabled, it will call `refreshNuxtData()` to re-fetch all data from the server.
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When preview mode is disabled, the composable will attach a callback to call `refreshNuxtData()` to run after a subsequent router navigation.
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You can specify custom callbacks to be triggered by providing your own functions for the `onEnable` and `onDisable` options.
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```js
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const { enabled, state } = usePreviewMode({
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onEnable: () => {
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console.log('preview mode has been enabled')
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},
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onDisable: () => {
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console.log('preview mode has been disabled')
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}
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})
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```
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## Example
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The example below creates a page where part of a content is rendered only in preview mode.
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```vue [pages/some-page.vue]
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<script setup>
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const { enabled, state } = usePreviewMode()
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const { data } = await useFetch('/api/preview', {
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query: {
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apiKey: state.token
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}
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})
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</script>
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<template>
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<div>
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Some base content
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<p v-if="enabled">
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Only preview content: {{ state.token }}
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<br>
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<button @click="enabled = false">
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disable preview mode
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</button>
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</p>
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</div>
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</template>
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```
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Now you can generate your site and serve it:
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```bash [Terminal]
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npx nuxi generate
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npx nuxi preview
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```
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Then you can see your preview page by adding the query param `preview` to the end of the page you want to see once:
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```js
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?preview=true
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```
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::note
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`usePreviewMode` should be tested locally with `nuxi generate` and then `nuxi preview` rather than `nuxi dev`. (The [preview command](/docs/api/commands/preview) is not related to preview mode.)
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::
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