Actions

Added in: astro@4.15

Astro Actions allow you to define and call backend functions with type-safety. Actions perform data fetching, JSON parsing, and input validation for you. This can greatly reduce the amount of boilerplate needed compared to using an API endpoint.

Use actions instead of API endpoints for seamless communication between your client and server code and to:

• Automatically validate JSON and form data inputs using Zod validation.
• Generate type-safe functions to call your backend from the client and even from HTML form actions. No need for manual fetch() calls.
• Standardize backend errors with the ActionError object.

Basic usage

Section titled Basic usage

Actions are defined in a server object exported from src/actions/index.ts:

src/actions/index.ts

import { defineAction } from 'astro:actions';
import { z } from 'astro:schema';

export const server = {
  myAction: defineAction({ /* ... */ })
}

Your actions are available as functions from the astro:actions module. Import actions and call them client-side within a UI framework component, a form POST request, or by using a <script> tag in an Astro component.

When you call an action, it returns an object with either data containing the JSON-serialized result, or error containing thrown errors.

src/pages/index.astro

---
---

<script>
import { actions } from 'astro:actions';

async () => {
  const { data, error } = await actions.myAction({ /* ... */ });
}
</script>

Write your first action

Section titled Write your first action

Follow these steps to define an action and call it in a script tag in your Astro page.

1. Create a src/actions/index.ts file and export a server object.

   src/actions/index.ts

   export const server = {
     // action declarations
   }

2. Import the defineAction() utility from astro:actions, and the z object from astro:schema.

   src/actions/index.ts

   import { defineAction } from 'astro:actions';
   import { z } from 'astro:schema';
   
    export const server = {
     // action declarations
   }

3. Use the defineAction() utility to define a getGreeting action. The input property will be used to validate input parameters with a Zod schema and the handler() function includes the backend logic to run on the server.

   src/actions/index.ts

   import { defineAction } from 'astro:actions';
   import { z } from 'astro:schema';
   
   export const server = {
     getGreeting: defineAction({
       input: z.object({
         name: z.string(),
       }),
       handler: async (input) => {
         return `Hello, ${input.name}!`
       }
     })
   }

4. Create an Astro component with a button that will fetch a greeting using your getGreeting action when clicked.

   src/pages/index.astro

   ---
   ---
   
   <button>Get greeting</button>
   
   <script>
   const button = document.querySelector('button');
   button?.addEventListener('click', async () => {
     // Show alert pop-up with greeting from action
   });
   </script>

5. To use your action, import actions from astro:actions and then call actions.getGreeting() in the click handler. The name option will be sent to your action’s handler() on the server and, if there are no errors, the result will be available as the data property.

   src/pages/index.astro

   ---
   ---
   
   <button>Get greeting</button>
   
   <script>
   import { actions } from 'astro:actions';
   
   const button = document.querySelector('button');
   button?.addEventListener('click', async () => {
     // Show alert pop-up with greeting from action
     const { data, error } = await actions.getGreeting({ name: "Houston" });
     if (!error) alert(data);
   })
   </script>

See the full Actions API documentation for details on defineAction() and its properties.

Organizing actions

Section titled Organizing actions

All actions in your project must be exported from the server object in the src/actions/index.ts file. You can define actions inline or you can move action definitions to separate files and import them. You can even group related functions in nested objects.

For example, to colocate all of your user actions, you can create a src/actions/user.ts file and nest the definitions of both getUser and createUser inside a single user object.

src/actions/user.ts

import { defineAction } from 'astro:actions';

export const user = {
  getUser: defineAction(/* ... */),
  createUser: defineAction(/* ... */),
}

Then, you can import this user object into your src/actions/index.ts file and add it as a top-level key to the server object alongside any other actions:

src/actions/index.ts

import { user } from './user';

export const server = {
  myAction: defineAction({ /* ... */ }),
  user,
}

Now, all of your user actions are callable from the actions.user object:

• actions.user.getUser()
• actions.user.createUser()

Handling returned data

Section titled Handling returned data

Actions return an object containing either data with the type-safe return value of your handler(), or an error with any backend errors. Errors may come from validation errors on the input property or thrown errors within the handler().

Checking for errors

Section titled Checking for errors

It’s best to check if an error is present before using the data property. This allows you to handle errors in advance and ensures data is defined without an undefined check.

const { data, error } = await actions.example();

if (error) {
  // handle error cases
  return;
}
// use `data`

Accessing data directly without an error check

Section titled Accessing data directly without an error check

To skip error handling, for example while prototyping or using a library that will catch errors for you, use the .orThrow() property on your action call to throw errors instead of returning an error. This will return the action’s data directly.

This example calls a likePost() action that returns the updated number of likes as a number from the action handler:

const updatedLikes = await actions.likePost.orThrow({ postId: 'example' });
//    ^ type: number

Handling backend errors in your action

Section titled Handling backend errors in your action

You can use the provided ActionError to throw an error from your action handler(), such as “not found” when a database entry is missing, or “unauthorized” when a user is not logged in. This has two main benefits over returning undefined:

• You can set a status code like 404 - Not found or 401 - Unauthorized. This improves debugging errors in both development and in production by letting you see the status code of each request.

• In your application code, all errors are passed to the error object on an action result. This avoids the need for undefined checks on data, and allows you to display targeted feedback to the user depending on what went wrong.

Creating an ActionError

Section titled Creating an ActionError

To throw an error, import the ActionError() class from the astro:actions module. Pass it a human-readable status code (e.g. "NOT_FOUND" or "BAD_REQUEST"), and an optional message to provide further information about the error.

This example throws an error from a likePost action when a user is not logged in, after checking a hypothetical “user-session” cookie for authentication:

src/actions/index.ts

import { defineAction, ActionError } from "astro:actions";
import { z } from "astro:schema";

export const server = {
  likePost: defineAction({
    input: z.object({ postId: z.string() }),
    handler: async (input, ctx) => {
      if (!ctx.cookies.has('user-session')) {
        throw new ActionError({
          code: "UNAUTHORIZED",
          message: "User must be logged in.",
        });
      }
      // Otherwise, like the post
    },
  }),
};

Handling an ActionError

Section titled Handling an ActionError

To handle this error, you can call the action from your application and check whether an error property is present. This property will be of type ActionError and will contain your code and message.

In the following example, a LikeButton.tsx component calls the likePost() action when clicked. If an authentication error occurs, the error.code attribute is used to determine whether to display a login link:

src/components/LikeButton.tsx

import { actions } from 'astro:actions';
import { useState } from 'preact/hooks';

export function LikeButton({ postId }: { postId: string }) {
  const [showLogin, setShowLogin] = useState(false);
  return (
    <>
      {
        showLogin && <a href="/signin">Log in to like a post.</a>
      }
      <button onClick={async () => {
        const { data, error } = await actions.likePost({ postId });
        if (error?.code === 'UNAUTHORIZED') setShowLogin(true);
        // Early return for unexpected errors
        else if (error) return;
        // update likes
      }}>
        Like
      </button>
    </>
  )
}

Handling client redirects

Section titled Handling client redirects

When calling actions from the client, you can integrate with a client-side library like react-router, or you can use Astro’s navigate() function to redirect to a new page when an action succeeds.

This example navigates to the homepage after a logout action returns successfully:

src/pages/LogoutButton.tsx

import { actions } from 'astro:actions';
import { navigate } from 'astro:transitions/client';

export function LogoutButton() {
  return (
    <button onClick={async () => {
      const { error } = await actions.logout();
      if (!error) navigate('/');
    }}>
      Logout
    </button>
  );
}

Accepting form data from an action

Section titled Accepting form data from an action

Actions accept JSON data by default. To accept form data from an HTML form, set accept: 'form' in your defineAction() call:

src/actions/index.ts

import { defineAction } from 'astro:actions';
import { z } from 'astro:schema';

export const server = {
  comment: defineAction({
    accept: 'form',
    input: z.object(/* ... */),
    handler: async (input) => { /* ... */ },
  })
}

Validating form data

Section titled Validating form data

Actions will parse submitted form data to an object, using the value of each input’s name attribute as the object keys. For example, a form containing <input name="search"> will be parsed to an object like { search: 'user input' }. Your action’s input schema will be used to validate this object.

To receive the raw FormData object in your action handler instead of a parsed object, omit the input property in your action definition.

The following example shows a validated newsletter registration form that accepts a user’s email and requires a “terms of service” agreement checkbox.

1. Create an HTML form component with unique name attributes on each input:

   src/components/Newsletter.astro

   <form>
     <label for="email">E-mail</label>
     <input id="email" required type="email" name="email" />
     <label>
       <input required type="checkbox" name="terms">
       I agree to the terms of service
     </label>
     <button>Sign up</button>
   </form>

2. Define a newsletter action to handle the submitted form. Validate the email field using the z.string().email() validator, and the terms checkbox using z.boolean():

   src/actions/index.ts

   import { defineAction } from 'astro:actions';
   import { z } from 'astro:schema';
   
   export const server = {
     newsletter: defineAction({
       accept: 'form',
       input: z.object({
         email: z.string().email(),
         terms: z.boolean(),
       }),
       handler: async ({ email, terms }) => { /* ... */ },
     })
   }

   See the input API reference for all available form validators.

3. Add a <script> to the HTML form to submit the user input. This example overrides the form’s default submit behavior to call actions.newsletter(), and redirects to /confirmation using the navigate() function:

   src/components/Newsletter.astro

   <form>
     <label for="email">E-mail</label>
     <input id="email" required type="email" name="email" />
     <label>
       <input required type="checkbox" name="terms">
       I agree to the terms of service
     </label>
     <button>Sign up</button>
   </form>
   
   <script>
     import { actions } from 'astro:actions';
     import { navigate } from 'astro:transitions/client';
   
     const form = document.querySelector('form');
     form?.addEventListener('submit', async (event) => {
       event.preventDefault();
       const formData = new FormData(form);
       const { error } = await actions.newsletter(formData);
       if (!error) navigate('/confirmation');
     })
   </script>

   See “Call actions from an HTML form action” for an alternative way to submit form data.

Displaying form input errors

Section titled Displaying form input errors

You can validate form inputs before submission using native HTML form validation attributes like required, type="email", and pattern. For more complex input validation on the backend, you can use the provided isInputError() utility function.

To retrieve input errors, use the isInputError() utility to check whether an error was caused by invalid input. Input errors contain a fields object with messages for each input name that failed to validate. You can use these messages to prompt your user to correct their submission.

The following example checks the error with isInputError(), then checks whether the error is in the email field, before finally creating a message from the errors. You can use JavaScript DOM manipulation or your preferred UI framework to display this message to users.

import { actions, isInputError } from 'astro:actions';

const form = document.querySelector('form');
const formData = new FormData(form);
const { error } = await actions.newsletter(formData);
if (isInputError(error)) {
  // Handle input errors.
  if (error.fields.email) {
    const message = error.fields.email.join(', ');
  }
}

Call actions from an HTML form action

Section titled Call actions from an HTML form action

Note

Pages must be on-demand rendered when calling actions using a form action. Ensure prerendering is disabled on the page before using this API.

You can enable zero-JS form submissions with standard attributes on any <form> element. Form submissions without client-side JavaScript may be useful both as a fallback for when JavaScript fails to load, or if you prefer to handle forms entirely from the server.

Calling Astro.getActionResult() on the server returns the result of your form submission (data or error), and can be used to dynamically redirect, handle form errors, update the UI, and more.

To call an action from an HTML form, add method="POST" to your <form>, then set the form’s action attribute using your action, for example action={actions.logout}. This will set the action attribute to use a query string that is handled by the server automatically.

For example, this Astro component calls the logout action when the button is clicked and reloads the current page:

src/components/LogoutButton.astro

---
import { actions } from 'astro:actions';
---

<form method="POST" action={actions.logout}>
  <button>Log out</button>
</form>

Redirect on action success

Section titled Redirect on action success

To navigate to a different page when an action is successful without client-side JavaScript, you can prepend a path in the action attribute.

For example, action={'/confirmation' + actions.newsletter} will navigate to /confirmation when the newsletter action succeeds:

src/components/NewsletterSignup.astro

---
import { actions } from 'astro:actions';
---

<form method="POST" action={'/confirmation' + actions.newsletter}>
  <label>E-mail <input required type="email" name="email" /></label>
  <button>Sign up</button>
</form>

Dynamic redirect on action success

Section titled Dynamic redirect on action success

If you need to decide where to redirect to dynamically, you can use an action’s result on the server. A common example is creating a product record and redirecting to the new product’s page, e.g. /products/[id].

For example, say you have a createProduct action that returns the generated product id:

src/actions/index.ts

import { defineAction } from 'astro:actions';
import { z } from 'astro:schema';

export const server = {
  createProduct: defineAction({
    accept: 'form',
    input: z.object({ /* ... */ }),
    handler: async (input) => {
      const product = await persistToDatabase(input);
      return { id: product.id };
    },
  })
}

You can retrieve the action result from your Astro component by calling Astro.getActionResult(). This returns an object containing data or error properties when an action is called, or undefined if the action was not called during this request.

Use the data property to construct a URL to use with Astro.redirect():

src/pages/products/create.astro

---
import { actions } from 'astro:actions';

const result = Astro.getActionResult(actions.createProduct);
if (result && !result.error) {
  return Astro.redirect(`/products/${result.data.id}`);
}
---

<form method="POST" action={actions.createProduct}>
  <!--...-->
</form>

Handle form action errors

Section titled Handle form action errors

Astro will not redirect to your action route when an action fails. Instead, the current page is reloaded with any errors the action returned. Calling Astro.getActionResult() in the Astro component containing your form gives you access to the error object for custom error handling.

The following example displays a general failure message when a newsletter action fails:

src/pages/index.astro

---
import { actions } from 'astro:actions';

const result = Astro.getActionResult(actions.newsletter);
---

{result?.error && (
  <p class="error">Unable to sign up. Please try again later.</p>
)}
<form method="POST" action={'/confirmation' + actions.newsletter}>
  <label>
    E-mail
    <input required type="email" name="email" />
  </label>
  <button>Sign up</button>
</form>

For more customization, you can use the isInputError() utility to check whether an error is caused by invalid input.

The following example renders an error banner under the email input field when an invalid email is submitted:

src/pages/index.astro

---
import { actions, isInputError } from 'astro:actions';

const result = Astro.getActionResult(actions.newsletter);
const inputErrors = isInputError(result?.error) ? result.error.fields : {};
---

<form method="POST" action={'/confirmation' + actions.newsletter}>
  <label>
    E-mail
    <input required type="email" name="email" aria-describedby="error" />
  </label>
  {inputErrors.email && <p id="error">{inputErrors.email.join(',')}</p>}
  <button>Sign up</button>
</form>

Note

Astro persists action data and error with a single-use cookie. This means getActionResult() will return a result on the first request only, and undefined when revisiting the page.

Preserve input values on error

Section titled Preserve input values on error

Inputs will be cleared whenever a form is submitted. To persist input values, you can enable view transitions on the page and apply the transition:persist directive to each input:

<input transition:persist required type="email" name="email" />

Update the UI with a form action result

Section titled Update the UI with a form action result

The result returned by Astro.getActionResult() is single-use, and will reset to undefined whenever the page is refreshed. This is ideal for displaying input errors and showing temporary notifications to the user on success.

Tip

If you need a result to be displayed across page refreshes, consider storing the result in a database or in a cookie.

Pass an action to Astro.getActionResult() and use the returned data property to render any temporary UI you want to display. This example uses the productName property returned by an addToCart action to show a success message:

src/pages/products/[slug].astro

---
import { actions } from 'astro:actions';

const result = Astro.getActionResult(actions.addToCart);
---

{result && !result.error && (
  <p class="success">Added {result.data.productName} to cart</p>
)}

<!--...-->

Caution

Action data is passed using a persisted cookie. This cookie is not encrypted and is limited to 4 KB in size, although the exact limit may vary between browsers.

In general, we recommend returning the minimum information required from your action handler to avoid vulnerabilities, and persist other sensitive information in a database.

For example, you might return the name of a product in an addToCart action, rather than returning the entire product object:

src/actions/index.ts

import { defineAction } from 'astro:actions';

export const server = {
  addToCart: defineAction({
    handler: async () => {
      /* ... */
      return product;
      return { productName: product.name };
    }
  })
}

Call actions from Astro components and server endpoints

Section titled Call actions from Astro components and server endpoints

You can call actions directly from Astro component scripts using the Astro.callAction() wrapper (or context.callAction() when using a server endpoint). This is common to reuse logic from your actions in other server code.

Pass the action as the first argument and any input parameters as the second argument. This returns the same data and error objects you receive when calling actions on the client:

src/pages/products.astro

---
import { actions } from 'astro:actions';

const searchQuery = Astro.url.searchParams.get('search');
if (searchQuery) {
  const { data, error } = Astro.callAction(actions.findProduct, { query: searchQuery });
  // handle result
}
---