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Preview

With the Preview feature, you can preview your front end application directly from Strapi's admin panel. This is helpful to see how updates to your content in the Edit View of the Content Manager will affect the final result.

IDENTITY CARD
Plan
Free feature.
Side panel available only with CMS Growth and Enterprise plans.
Role & permission
Read permissions in Roles > Plugins - Users & Permissions
Activation
Should be configured in the config/admin file
Environment
Available in both Development & Production environment
Previewing contentPreviewing content

Configuration​

Notes

  • The following environment variables must be defined in your .env file, replacing example values with appropriate values:

    CLIENT_URL=https://your-frontend-app.com
    PREVIEW_SECRET=your-secret-key

    The PREVIEW_SECRET key is optional but required with Next.js draft mode.

  • A front-end application for your Strapi project should be already created and set up.

Configuration components​

The Preview feature configuration is stored in the preview object of the config/admin file and consists of 3 key components:

Activation flag​

Enables or disables the preview feature:

config/admin.ts|js
// …
preview: {
  enabled: true,
    // …
}
// …

Allowed origins​

Controls which domains can access previews:

config/admin.ts|js
// …
preview: {
  enabled: true,
  config: {
    allowedOrigins: env("CLIENT_URL"),  // Usually your frontend application URL
    // …
  }
}
// …

Preview handler​

Manages the preview logic and URL generation, as in the following basic example where uid is the content-type identifier (e.g., api::article.article or plugin::my-api.my-content-type):

config/admin.ts|js
// …
preview: {
  enabled: true,
  config: {
    // …
    async handler(uid, { documentId, locale, status }) {
      const document = await strapi.documents(uid).findOne({ documentId });
      const pathname = getPreviewPathname(uid, { locale, document });

      return `${env('PREVIEW_URL')}${pathname}`
    },
  }
}
// …

An example of URL generation logic in given in the following basic implementation guide.

Previewing draft entries​

The strategy for the front end application to query draft or published content is framework-specific. At least 3 strategies exist:

  • using a query parameter, having something like /your-path?preview=true (this is, for instance, how Nuxt works)
  • redirecting to a dedicated preview route like /preview?path=your-path(this is, for instance, how Next's draft mode works)
  • or using a different domain for previews like preview.mysite.com/your-path.

When Draft & Publish is enabled for your content-type, you can also directly leverage Strapi's status parameter to handle the logic within the Preview handler, using the following generic approach:

async handler(uid, { documentId, locale, status }) {
   const document = await strapi.documents(uid).findOne({ documentId });
   const pathname = getPreviewPathname(uid, { locale, document });
   if (status === 'published')  { 
      // return the published version
   }
   // return the draft version
},

A more detailed example using the draft mode of Next.js is given in the basic implementation guide.

Basic implementation guide​

Follow these steps to add Preview capabilities to your content types.

1. [Strapi] Create the Preview configuration​

Create a new file /config/admin.ts (or update it if it exists) with the following basic structure:

config/admin.ts
export default ({ env }) => ({
  // Other admin-related configurations go here
  // (see docs.strapi.io/cms/configurations/admin-panel)
  preview: {
    enabled: true,
    config: {
      allowedOrigins: env('CLIENT_URL'),
      async handler (uid, { documentId, locale, status }) => {
        // Handler implementation coming in step 3
      },
    },
  },
});

2. [Strapi] Add URL generation logic​

Add the URL generation logic with a getPreviewPathname function. The following example is taken from the Launchpad Strapi demo application:

config/admin.ts
// Function to generate preview pathname based on content type and document
const getPreviewPathname = (uid, { locale, document }): string => {
  const { slug } = document;
  
  // Handle different content types with their specific URL patterns
  switch (uid) {
    // Handle pages with predefined routes
    case "api::page.page":
      switch (slug) {
        case "homepage":
          return `/${locale}`; // Localized homepage
        case "pricing":
          return "/pricing"; // Pricing page
        case "contact":
          return "/contact"; // Contact page
        case "faq":
          return "/faq"; // FAQ page
      }
    // Handle product pages
    case "api::product.product": {
      if (!slug) {
        return "/products"; // Products listing page
      }
      return `/products/${slug}`; // Individual product page
    }
    // Handle blog articles
    case "api::article.article": {
      if (!slug) {
        return "/blog"; // Blog listing page
      }
      return `/blog/${slug}`; // Individual article page
    }
    default: {
      return null;
    }
  }
};

// … main export (see step 3)
Note

Some content types don't need to have a preview if it doesn't make sense, hence the default case returning null. A Global single type with some site metadata, for example, will not have a matching front-end page. In these cases, the handler function should return null, and the preview UI will not be shown in the admin panel. This is how you enable or disable preview per content type.

3. [Strapi] Add handler logic​

Create the complete configuration, expanding the basic configuration created in step 1. with the URL generation logic created in step 2., adding an appropriate handler logic:

config/admin.ts
const getPreviewPathname = (uid, { locale, document }): string => {
  // … as defined in step 2
};

// Main configuration export
export default ({ env }) => {
  // Get environment variables
  const clientUrl = env("CLIENT_URL"); // Frontend application URL
  const previewSecret = env("PREVIEW_SECRET"); // Secret key for preview authentication

  return {
    // Other admin-related configurations go here
    // (see docs.strapi.io/cms/configurations/admin-panel)
    preview: {
      enabled: true, // Enable preview functionality
      config: {
        allowedOrigins: clientUrl, // Restrict preview access to specific domain
        async handler(uid, { documentId, locale, status }) {
          // Fetch the complete document from Strapi
          const document = await strapi.documents(uid).findOne({ documentId });
          
          // Generate the preview pathname based on content type and document
          const pathname = getPreviewPathname(uid, { locale, document });

          // Disable preview if the pathname is not found
          if (!pathname) {
            return null;
          }

          // Use Next.js draft mode passing it a secret key and the content-type status
          const urlSearchParams = new URLSearchParams({
            url: pathname,
            secret: previewSecret,
            status,
          });
          return `${clientUrl}/api/preview?${urlSearchParams}`;
        },
      },
    },
  };
};

4. [Front end] Set up the front-end preview route​

Setting up the front-end preview route is highly dependent on the framework used for your front-end application.

For instance, Next.js draft mode and Nuxt preview mode provide additional documentation on how to implement the front-end part in their respective documentations.

If using Next.js, a basic implementation could be like in the following example taken from the Launchpad Strapi demo application:

/next/api/preview/route.ts
import { draftMode } from "next/headers";
import { redirect } from "next/navigation";

export async function GET(request: Request) {
  // Parse query string parameters
  const { searchParams } = new URL(request.url);
  const secret = searchParams.get("secret");
  const url = searchParams.get("url");
  const status = searchParams.get("status");

  // Check the secret and next parameters
  // This secret should only be known to this route handler and the CMS
  if (secret !== process.env.PREVIEW_SECRET) {
    return new Response("Invalid token", { status: 401 });
  }

  // Enable Draft Mode by setting the cookie
  if (status === "published") {
    draftMode().disable();
  } else {
    draftMode().enable();
  }

  // Redirect to the path from the fetched post
  // We don't redirect to searchParams.slug as that might lead to open redirect vulnerabilities
  redirect(url || "/");
}

5. [Front end] Allow the front-end to be embedded​

On the Strapi side, the allowedOrigins configuration parameter allows the admin panel to load the front-end window in an iframe. But allowing the embedding works both ways, so on the front-end side, you also need to allow the window to be embedded in Strapi's admin panel.

This requires the front-end application to have its own header directive, the CSP frame-ancestors directive. Setting this directive up depends on how your website is built. For instance, setting this up in Next.js requires a middleware configuration (see Next.js docs).

6. [Front end] Detect changes in Strapi and refresh the front-end​

Strapi emits a strapiUpdate message to inform the front end that data has changed.

To track this, within your front-end application, add an event listener to listen to events posted through the postMessage() API on the window object. The listener needs to filter through messages and react only to Strapi-initiated messages, then refresh the iframe content.

With Next.js, the recommended way to refresh the iframe content is with the `router.refresh()` method.

next/app/path/to/your/front/end/logic.jsx
export default function MyClientComponent({...props}) {
  // …
  const router = useRouter();

  useEffect(() => {
    const handleMessage = async (message) => {
      if (
        // Filters events emitted through the postMessage() API
        message.origin === process.env.NEXT_PUBLIC_API_URL &&
        message.data.type === "strapiUpdate"
      ) { // Recommended way to refresh with Next.js
        router.refresh();
      }
    };

    // Add the event listener
    window.addEventListener("message", handleMessage);

    // Cleanup the event listener on unmount
    return () => {
      window.removeEventListener("message", handleMessage);
    };
  }, [router]);

  // ...
}
Caching in Next.js:

In Next.js, cache persistence may require additional steps. You might need to invalidate the cache by making an API call from the client side to the server, where the revalidation logic will be handled. Please refer to Next.js documentation for details, for instance with the revalidatePath() method.


[Front end] Next steps​

Once the preview system is set up, you need to adapt your data fetching logic to handle draft content appropriately. This involves the following steps:

  1. Create or adapt your data fetching utility to check if draft mode is enabled
  2. Update your API calls to include the draft status parameter when appropriate

The following, taken from the Launchpad Strapi demo application, is an example of how to implement draft-aware data fetching in your Next.js front-end application:

import { draftMode } from "next/headers";
import qs from "qs";

export default async function fetchContentType(
  contentType: string,
  params: Record = {}
): Promise {
  // Check if Next.js draft mode is enabled
  const { isEnabled: isDraftMode } = draftMode();
  
  try {
    const queryParams = { ...params };
    // Add status=draft parameter when draft mode is enabled
    if (isDraftMode) {
      queryParams.status = "draft";
    }
    
    const url = `${baseURL}/${contentType}?${qs.stringify(queryParams)}`;
    const response = await fetch(url);
    if (!response.ok) {
      throw new Error(
        `Failed to fetch data from Strapi (url=${url}, status=${response.status})`
      );
    }
    return await response.json();
  } catch (error) {
    console.error("Error fetching content:", error);
    throw error;
  }
}

This utility method can then be used in your page components to fetch either draft or published content based on the preview state:

// In your page component:
const pageData = await fetchContentType('api::page.page', {
  // Your other query parameters
});

6. [Front end] Detect changes in Strapi and refresh the front-end​

Strapi emits a strapiUpdate message to inform the front end that data has changed.

To track this, within your front-end application, add an event listener to listen to events posted through the postMessage() API on the window object. The listener needs to filter through messages and react only to Strapi-initiated messages, then refresh the iframe content.

With Next.js, the recommended way to refresh the iframe content is with the `router.refresh()` method.

next/app/path/to/your/front/end/logic.jsx
export default function MyClientComponent({...props}) {
  // …
  const router = useRouter();

  useEffect(() => {
    const handleMessage = async (message) => {
      if (
        // Filters events emitted through the postMessage() API
        message.origin === process.env.NEXT_PUBLIC_API_URL &&
        message.data.type === "strapiUpdate"
      ) { // Recommended way to refresh with Next.js
        router.refresh();
      }
    };

    // Add the event listener
    window.addEventListener("message", handleMessage);

    // Cleanup the event listener on unmount
    return () => {
      window.removeEventListener("message", handleMessage);
    };
  }, [router]);

  // ...
}
Caching in Next.js:

In Next.js, cache persistence may require additional steps. You might need to invalidate the cache by making an API call from the client side to the server, where the revalidation logic will be handled. Please refer to Next.js documentation for details, for instance with the revalidatePath() method.


[Front end] Next steps​

Once the preview system is set up, you need to adapt your data fetching logic to handle draft content appropriately. This involves the following steps:

  1. Create or adapt your data fetching utility to check if draft mode is enabled
  2. Update your API calls to include the draft status parameter when appropriate

The following, taken from the Launchpad Strapi demo application, is an example of how to implement draft-aware data fetching in your Next.js front-end application:

import { draftMode } from "next/headers";
import qs from "qs";

export default async function fetchContentType(
  contentType: string,
  params: Record = {}
): Promise {
  // Check if Next.js draft mode is enabled
  const { isEnabled: isDraftMode } = draftMode();
  
  try {
    const queryParams = { ...params };
    // Add status=draft parameter when draft mode is enabled
    if (isDraftMode) {
      queryParams.status = "draft";
    }
    
    const url = `${baseURL}/${contentType}?${qs.stringify(queryParams)}`;
    const response = await fetch(url);
    if (!response.ok) {
      throw new Error(
        `Failed to fetch data from Strapi (url=${url}, status=${response.status})`
      );
    }
    return await response.json();
  } catch (error) {
    console.error("Error fetching content:", error);
    throw error;
  }
}

This utility method can then be used in your page components to fetch either draft or published content based on the preview state:

// In your page component:
const pageData = await fetchContentType('api::page.page', {
  // Your other query parameters
});

Usage​

Path to use the feature: Content Manager, edit view of your content type

Preview with or without the side panel

Based on your CMS plan, your experience with Preview will be different:

Once the Preview feature is properly set up, an Open preview button is visible on the right side of the Content Manager's edit view. Clicking it will display the preview of your content as it will appear in your front-end application, but directly within Strapi's the admin panel.

Previewing contentPreviewing content

Once the Preview is open, you can:

  • click the close button in the upper left corner to go back to the Edit View of the Content Manager,
  • switch between previewing the draft and the published version (if Draft & Publish is enabled for the content-type),
  • and click the link icon in the upper right corner to copy the preview link. Depending on the preview tab you are currently viewing, this will either copy the link to the preview of the draft or the published version.

Additionally, you can:

Note

In the Edit view of the Content Manager, the Open preview button will be disabled if you have unsaved changes. Save your latest changes and you should be able to preview content again.

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