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--- |
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title: How to load and optimize scripts |
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nav_title: Scripts |
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description: Optimize 3rd party scripts with the built-in Script component. |
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related: |
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title: API Reference |
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description: Learn more about the next/script API. |
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links: |
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- app/api-reference/components/script |
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--- |
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{/* The content of this doc is shared between the app and pages router. You can use the `<PagesOnly>Content</PagesOnly>` component to add content that is specific to the Pages Router. Any shared content should not be wrapped in a component. */} |
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<AppOnly> |
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### Layout Scripts |
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To load a third-party script for multiple routes, import `next/script` and include the script directly in your layout component: |
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```tsx filename="app/dashboard/layout.tsx" switcher |
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import Script from 'next/script' |
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export default function DashboardLayout({ |
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children, |
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}: { |
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children: React.ReactNode |
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}) { |
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return ( |
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<> |
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<section>{children}</section> |
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<Script src="https://example.com/script.js" /> |
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</> |
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) |
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} |
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``` |
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```jsx filename="app/dashboard/layout.js" switcher |
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import Script from 'next/script' |
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export default function DashboardLayout({ children }) { |
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return ( |
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<> |
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<section>{children}</section> |
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<Script src="https://example.com/script.js" /> |
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</> |
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) |
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} |
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``` |
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The third-party script is fetched when the folder route (e.g. `dashboard/page.js`) or any nested route (e.g. `dashboard/settings/page.js`) is accessed by the user. Next.js will ensure the script will **only load once**, even if a user navigates between multiple routes in the same layout. |
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</AppOnly> |
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### Application Scripts |
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<AppOnly> |
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To load a third-party script for all routes, import `next/script` and include the script directly in your root layout: |
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```tsx filename="app/layout.tsx" switcher |
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import Script from 'next/script' |
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export default function RootLayout({ |
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children, |
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}: { |
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children: React.ReactNode |
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}) { |
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return ( |
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<html lang="en"> |
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<body>{children}</body> |
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<Script src="https://example.com/script.js" /> |
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</html> |
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) |
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} |
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``` |
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```jsx filename="app/layout.js" switcher |
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import Script from 'next/script' |
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export default function RootLayout({ children }) { |
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return ( |
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<html lang="en"> |
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<body>{children}</body> |
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<Script src="https://example.com/script.js" /> |
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</html> |
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) |
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} |
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``` |
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</AppOnly> |
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<PagesOnly> |
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To load a third-party script for all routes, import `next/script` and include the script directly in your custom `_app`: |
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```jsx filename="pages/_app.js" |
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import Script from 'next/script' |
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export default function MyApp({ Component, pageProps }) { |
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return ( |
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<> |
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<Component {...pageProps} /> |
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<Script src="https://example.com/script.js" /> |
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</> |
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) |
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} |
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``` |
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</PagesOnly> |
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This script will load and execute when _any_ route in your application is accessed. Next.js will ensure the script will **only load once**, even if a user navigates between multiple pages. |
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> **Recommendation**: We recommend only including third-party scripts in specific pages or layouts in order to minimize any unnecessary impact to performance. |
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### Strategy |
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Although the default behavior of `next/script` allows you to load third-party scripts in any page or layout, you can fine-tune its loading behavior by using the `strategy` property: |
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- `beforeInteractive`: Load the script before any Next.js code and before any page hydration occurs. |
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- `afterInteractive`: (**default**) Load the script early but after some hydration on the page occurs. |
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- `lazyOnload`: Load the script later during browser idle time. |
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- `worker`: (experimental) Load the script in a web worker. |
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Refer to the [`next/script`](/docs/app/api-reference/components/script#strategy) API reference documentation to learn more about each strategy and their use cases. |
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### Offloading Scripts To A Web Worker (experimental) |
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> **Warning:** The `worker` strategy is not yet stable and does not yet work with the App Router. Use with caution. |
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Scripts that use the `worker` strategy are offloaded and executed in a web worker with [Partytown](https://partytown.builder.io/). This can improve the performance of your site by dedicating the main thread to the rest of your application code. |
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This strategy is still experimental and can only be used if the `nextScriptWorkers` flag is enabled in `next.config.js`: |
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```js filename="next.config.js" |
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module.exports = { |
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experimental: { |
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nextScriptWorkers: true, |
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}, |
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} |
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``` |
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Then, run `next` (normally `npm run dev` or `yarn dev`) and Next.js will guide you through the installation of the required packages to finish the setup: |
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```bash filename="Terminal" |
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npm run dev |
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``` |
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You'll see instructions like these: Please install Partytown by running `npm install @builder.io/partytown` |
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Once setup is complete, defining `strategy="worker"` will automatically instantiate Partytown in your application and offload the script to a web worker. |
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```tsx filename="pages/home.tsx" switcher |
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import Script from 'next/script' |
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export default function Home() { |
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return ( |
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<> |
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<Script src="https://example.com/script.js" strategy="worker" /> |
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</> |
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) |
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} |
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``` |
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```jsx filename="pages/home.js" switcher |
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import Script from 'next/script' |
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export default function Home() { |
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return ( |
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<> |
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<Script src="https://example.com/script.js" strategy="worker" /> |
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</> |
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) |
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} |
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``` |
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There are a number of trade-offs that need to be considered when loading a third-party script in a web worker. Please see Partytown's [tradeoffs](https://partytown.builder.io/trade-offs) documentation for more information. |
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<PagesOnly> |
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#### Using custom Partytown configuration |
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Although the `worker` strategy does not require any additional configuration to work, Partytown supports the use of a config object to modify some of its settings, including enabling `debug` mode and forwarding events and triggers. |
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If you would like to add additional configuration options, you can include it within the `<Head />` component used in a [custom `_document.js`](/docs/pages/building-your-application/routing/custom-document): |
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```jsx filename="_pages/document.jsx" |
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import { Html, Head, Main, NextScript } from 'next/document' |
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export default function Document() { |
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return ( |
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<Html> |
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<Head> |
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<script |
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data-partytown-config |
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dangerouslySetInnerHTML={{ |
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__html: ` |
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partytown = { |
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lib: "/_next/static/~partytown/", |
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debug: true |
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}; |
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`, |
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}} |
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/> |
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</Head> |
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<body> |
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<Main /> |
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<NextScript /> |
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</body> |
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</Html> |
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) |
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} |
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``` |
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In order to modify Partytown's configuration, the following conditions must be met: |
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1. The `data-partytown-config` attribute must be used in order to overwrite the default configuration used by Next.js |
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2. Unless you decide to save Partytown's library files in a separate directory, the `lib: "/_next/static/~partytown/"` property and value must be included in the configuration object in order to let Partytown know where Next.js stores the necessary static files. |
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> **Note**: If you are using an [asset prefix](/docs/pages/api-reference/config/next-config-js/assetPrefix) and would like to modify Partytown's default configuration, you must include it as part of the `lib` path. |
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Take a look at Partytown's [configuration options](https://partytown.builder.io/configuration) to see the full list of other properties that can be added. |
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</PagesOnly> |
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### Inline Scripts |
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Inline scripts, or scripts not loaded from an external file, are also supported by the Script component. They can be written by placing the JavaScript within curly braces: |
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```jsx |
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<Script id="show-banner"> |
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{`document.getElementById('banner').classList.remove('hidden')`} |
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</Script> |
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``` |
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Or by using the `dangerouslySetInnerHTML` property: |
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```jsx |
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<Script |
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id="show-banner" |
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dangerouslySetInnerHTML={{ |
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__html: `document.getElementById('banner').classList.remove('hidden')`, |
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}} |
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/> |
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``` |
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> **Warning**: An `id` property must be assigned for inline scripts in order for Next.js to track and optimize the script. |
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### Executing Additional Code |
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Event handlers can be used with the Script component to execute additional code after a certain event occurs: |
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- `onLoad`: Execute code after the script has finished loading. |
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- `onReady`: Execute code after the script has finished loading and every time the component is mounted. |
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- `onError`: Execute code if the script fails to load. |
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<AppOnly> |
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These handlers will only work when `next/script` is imported and used inside of a [Client Component](/docs/app/getting-started/server-and-client-components) where `"use client"` is defined as the first line of code: |
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```tsx filename="app/page.tsx" switcher |
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'use client' |
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import Script from 'next/script' |
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export default function Page() { |
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return ( |
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<> |
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<Script |
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src="https://example.com/script.js" |
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onLoad={() => { |
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console.log('Script has loaded') |
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}} |
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/> |
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</> |
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) |
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} |
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``` |
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```jsx filename="app/page.js" switcher |
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'use client' |
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import Script from 'next/script' |
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export default function Page() { |
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return ( |
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<> |
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<Script |
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src="https://example.com/script.js" |
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onLoad={() => { |
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console.log('Script has loaded') |
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}} |
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/> |
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</> |
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) |
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} |
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``` |
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Refer to the [`next/script`](/docs/app/api-reference/components/script#onload) API reference to learn more about each event handler and view examples. |
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</AppOnly> |
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<PagesOnly> |
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These handlers will only work when `next/script` is imported and used inside of a [Client Component](/docs/app/getting-started/server-and-client-components) where `"use client"` is defined as the first line of code: |
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```tsx filename="pages/index.tsx" switcher |
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import Script from 'next/script' |
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export default function Page() { |
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return ( |
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<> |
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<Script |
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src="https://example.com/script.js" |
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onLoad={() => { |
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console.log('Script has loaded') |
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}} |
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/> |
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</> |
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) |
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} |
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``` |
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```jsx filename="pages/index.js" switcher |
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import Script from 'next/script' |
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export default function Page() { |
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return ( |
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<> |
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<Script |
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src="https://example.com/script.js" |
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onLoad={() => { |
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console.log('Script has loaded') |
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}} |
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/> |
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</> |
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) |
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} |
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``` |
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Refer to the [`next/script`](/docs/pages/api-reference/components/script#onload) API reference to learn more about each event handler and view examples. |
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</PagesOnly> |
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### Additional Attributes |
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There are many DOM attributes that can be assigned to a `<script>` element that are not used by the Script component, like [`nonce`](https://developer.mozilla.org/docs/Web/HTML/Global_attributes/nonce) or [custom data attributes](https://developer.mozilla.org/docs/Web/HTML/Global_attributes/data-*). Including any additional attributes will automatically forward it to the final, optimized `<script>` element that is included in the HTML. |
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<AppOnly> |
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```tsx filename="app/page.tsx" switcher |
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import Script from 'next/script' |
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export default function Page() { |
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return ( |
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<> |
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<Script |
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src="https://example.com/script.js" |
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id="example-script" |
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nonce="XUENAJFW" |
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data-test="script" |
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/> |
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</> |
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) |
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} |
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``` |
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```jsx filename="app/page.js" switcher |
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import Script from 'next/script' |
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export default function Page() { |
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return ( |
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<> |
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<Script |
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src="https://example.com/script.js" |
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id="example-script" |
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nonce="XUENAJFW" |
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data-test="script" |
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/> |
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</> |
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) |
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} |
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``` |
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</AppOnly> |
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<PagesOnly> |
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```tsx filename="pages/index.tsx" switcher |
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import Script from 'next/script' |
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export default function Page() { |
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return ( |
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<> |
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<Script |
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src="https://example.com/script.js" |
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id="example-script" |
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nonce="XUENAJFW" |
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data-test="script" |
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/> |
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</> |
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) |
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} |
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``` |
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```jsx filename="pages/index.js" switcher |
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import Script from 'next/script' |
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export default function Page() { |
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return ( |
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<> |
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<Script |
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src="https://example.com/script.js" |
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id="example-script" |
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nonce="XUENAJFW" |
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data-test="script" |
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/> |
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</> |
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) |
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} |
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``` |
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</PagesOnly> |
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