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API Reference

Astro global

Section titled Astro global

The Astro global is available in all contexts in .astro files. It has the following functions:

Astro.glob()

Section titled Astro.glob()

Astro.glob() is a way to load many local files into your static site setup.

src/components/my-component.astro
---
const posts = await Astro.glob('../pages/post/*.md'); // returns an array of posts that live at ./src/pages/post/*.md
---


<div>
{posts.slice(0, 3).map((post) => (
  <article>
    <h2>{post.frontmatter.title}</h2>
    <p>{post.frontmatter.description}</p>
    <a href={post.url}>Read more</a>
  </article>
))}
</div>

.glob() only takes one parameter: a relative URL glob of which local files you’d like to import. It’s asynchronous, and returns an array of the exports from matching files.

.glob() can’t take variables or strings that interpolate them, as they aren’t statically analyzable. (See the troubleshooting guide for a workaround.) This is because Astro.glob() is a wrapper of Vite’s import.meta.glob().

Markdown Files

Section titled Markdown Files

Markdown files loaded with Astro.glob() return the following MarkdownInstance interface:

export interface MarkdownInstance<T extends Record<string, any>> {
  /* Any data specified in this file's YAML frontmatter */
  frontmatter: T;
  /* The absolute file path of this file */
  file: string;
  /* The rendered path of this file */
  url: string | undefined;
  /* Astro Component that renders the contents of this file */
  Content: AstroComponentFactory;
  /** (Markdown only) Raw Markdown file content, excluding layout HTML and YAML frontmatter */
  rawContent(): string;
  /** (Markdown only) Markdown file compiled to HTML, excluding layout HTML */
  compiledContent(): string;
  /* Function that returns an array of the h1...h6 elements in this file */
  getHeadings(): Promise<{ depth: number; slug: string; text: string }[]>;
  default: AstroComponentFactory;
}

You can optionally provide a type for the frontmatter variable using a TypeScript generic.

---
interface Frontmatter {
  title: string;
  description?: string;
}
const posts = await Astro.glob<Frontmatter>('../pages/post/*.md');
---


<ul>
  {posts.map(post => <li>{post.frontmatter.title}</li>)}
</ul>

Astro Files

Section titled Astro Files

Astro files have the following interface:

export interface AstroInstance {
  /* The file path of this file */
  file: string;
  /* The URL for this file (if it is in the pages directory) */
  url: string | undefined;
  default: AstroComponentFactory;
}

Other Files

Section titled Other Files

Other files may have various different interfaces, but Astro.glob() accepts a TypeScript generic if you know exactly what an unrecognized file type contains.

---
interface CustomDataFile {
  default: Record<string, any>;
}
const data = await Astro.glob<CustomDataFile>('../data/**/*.js');
---

Astro.props

Section titled Astro.props

Astro.props is an object containing any values that have been passed as component attributes. Layout components for .md and .mdx files receive frontmatter values as props.

src/components/Heading.astro
---
const { title, date } = Astro.props;
---
<div>
  <h1>{title}</h1>
  <p>{date}</p>
</div>
src/pages/index.astro
---
import Heading from '../components/Heading.astro';
---
<Heading title="My First Post" date="09 Aug 2022" />
Learn more about how Markdown and MDX Layouts handle props.
Learn how to add TypeScript type definitions for your props.

Astro.params

Section titled Astro.params

Astro.params is an object containing the values of dynamic route segments matched for this request.

In static builds, this will be the params returned by getStaticPaths() used for prerendering dynamic routes.

In SSR builds, this can be any value matching the path segments in the dynamic route pattern.

src/pages/posts/[id].astro
---
export function getStaticPaths() {
  return [
    { params: { id: '1' } },
    { params: { id: '2' } },
    { params: { id: '3' } }
  ];
}


const { id } = Astro.params;
---
<h1>{id}</h1>

See also: params

Astro.request

Section titled Astro.request

Type: Request

Astro.request is a standard Request object. It can be used to get the url, headers, method, and even body of the request.

<p>Received a {Astro.request.method} request to "{Astro.request.url}".</p>
<p>Received request headers: <code>{JSON.stringify(Object.fromEntries(Astro.request.headers))}</code>

See also: Astro.url

Astro.response

Section titled Astro.response

Type: ResponseInit & { readonly headers: Headers }

Astro.response is a standard ResponseInit object. It has the following structure.

  • status: The numeric status code of the response, e.g., 200.
  • statusText: The status message associated with the status code, e.g., 'OK'.
  • headers: A Headers instance that you can use to set the HTTP headers of the response.

Astro.response is used to set the status, statusText, and headers for a page’s response.

---
if(condition) {
  Astro.response.status = 404;
  Astro.response.statusText = 'Not found';
}
---

Or to set a header:

---
Astro.response.headers.set('Set-Cookie', 'a=b; Path=/;');
---

Astro.cookies

Section titled Astro.cookies

Type: AstroCookies

Added in: astro@1.4.0

Astro.cookies contains utilities for reading and manipulating cookies in server-side rendering mode.

get
Section titled get

Type: (key: string, options?: AstroCookieGetOptions) => AstroCookie | undefined

Gets the cookie as an AstroCookie object, which contains the value and utility functions for converting the cookie to non-string types.

has
Section titled has

Type: (key: string, options?: AstroCookieGetOptions) => boolean

Whether this cookie exists. If the cookie has been set via Astro.cookies.set() this will return true, otherwise it will check cookies in the Astro.request.

set
Section titled set

Type: (key: string, value: string | object, options?: AstroCookieSetOptions) => void

Sets the cookie key to the given value. This will attempt to convert the cookie value to a string. Options provide ways to set cookie features, such as the maxAge or httpOnly.

delete
Section titled delete

Type: (key: string, options?: AstroCookieDeleteOptions) => void

Invalidates a cookie by setting the expiration date in the past (0 in Unix time).

Once a cookie is “deleted” (expired), Astro.cookies.has() will return false and Astro.cookies.get() will return an AstroCookie with a value of undefined. Options available when deleting a cookie are: domain, path, httpOnly, sameSite, and secure.

merge
Section titled merge

Type: (cookies: AstroCookies) => void

Merges a new AstroCookies instance into the current instance. Any new cookies will be added to the current instance and any cookies with the same name will overwrite existing values.

headers
Section titled headers

Type: () => Iterator<string>

Gets the header values for Set-Cookie that will be sent out with the response.

AstroCookie

Section titled AstroCookie

Getting a cookie via Astro.cookies.get() returns a AstroCookie type. It has the following structure.

value
Section titled value

Type: string

The raw string value of the cookie.

json
Section titled json

Type: () => Record<string, any>

Parses the cookie value via JSON.parse(), returning an object. Throws if the cookie value is not valid JSON.

number
Section titled number

Type: () => number

Parses the cookie value as a Number. Returns NaN if not a valid number.

boolean
Section titled boolean

Type: () => boolean

Converts the cookie value to a boolean.

AstroCookieGetOptions

Section titled AstroCookieGetOptions

Added in: astro@4.1.0

Getting a cookie also allows specifying options via the AstroCookieGetOptions interface:

decode
Section titled decode

Type: (value: string) => string

Allows customization of how a cookie is deserialized into a value.

AstroCookieSetOptions

Section titled AstroCookieSetOptions

Added in: astro@4.1.0

Setting a cookie via Astro.cookies.set() allows passing in a AstroCookieSetOptions to customize how the cookie is serialized.

domain
Section titled domain

Type: string

Specifies the domain. If no domain is set, most clients will interpret to apply to the current domain.

expires
Section titled expires

Type: Date

Specifies the date on which the cookie will expire.

httpOnly
Section titled httpOnly

Type: boolean

If true, the cookie will not be accessible client-side.

maxAge
Section titled maxAge

Type: number

Specifies a number, in seconds, for which the cookie is valid.

path
Section titled path

Type: string

Specifies a subpath of the domain in which the cookie is applied.

sameSite
Section titled sameSite

Type: boolean | 'lax' | 'none' | 'strict'

Specifies the value of the SameSite cookie header.

secure
Section titled secure

Type: boolean

If true, the cookie is only set on https sites.

encode
Section titled encode

Type: (value: string) => string

Allows customizing how the cookie is serialized.

Astro.redirect()

Section titled Astro.redirect()

Type: (path: string, status?: number) => Response

Allows you to redirect to another page, and optionally provide an HTTP response status code as a second parameter.

A page (and not a child component) must return the result of Astro.redirect() for the redirect to occur.

For statically-generated sites, this will produce a client redirect using a <meta http-equiv="refresh"> tag and does not support status codes.

When using an on-demand rendering mode, status codes are supported. Astro will serve redirected requests with a default HTTP response status of 302 unless another code is specified.

The following example redirects a user to a login page:

src/pages/account.astro
---
import { isLoggedIn } from '../utils';


const cookie = Astro.request.headers.get('cookie');


// If the user is not logged in, redirect them to the login page
if (!isLoggedIn(cookie)) {
  return Astro.redirect('/login');
}
---

Astro.rewrite()

Section titled Astro.rewrite()

Type: (rewritePayload: string | URL | Request) => Promise<Response>

Added in: astro@4.13.0

Allows you to serve content from a different URL or path without redirecting the browser to a new page.

The method accepts either a string, a URL, or a Request for the location of the path.

Use a string to provide an explicit path:

src/pages/index.astro
---
return Astro.rewrite("/login")
---

Use a URL type when you need to construct the URL path for the rewrite. The following example renders a page’s parent path by creating a new URL from the relative "../" path:

src/pages/blog/index.astro
---
return Astro.rewrite(new URL("../", Astro.url))
---

Use a Request type for complete control of the Request sent to the server for the new path. The following example sends a request to render the parent page while also providing headers:

src/pages/blog/index.astro
---
return Astro.rewrite(new Request(new URL("../", Astro.url), {
  headers: {
    "x-custom-header": JSON.stringify(Astro.locals.someValue)
  }
}))
---

Astro.url

Section titled Astro.url

Type: URL

Added in: astro@1.0.0-rc

A URL object constructed from the current Astro.request.url URL string value. Useful for interacting with individual properties of the request URL, like pathname and origin.

Equivalent to doing new URL(Astro.request.url).

Astro.url will be localhost in dev mode if site is not configured for static sites, and for on-demand rendered sites using server or hybrid output.

<h1>The current URL is: {Astro.url}</h1>
<h1>The current URL pathname is: {Astro.url.pathname}</h1>
<h1>The current URL origin is: {Astro.url.origin}</h1>

You can also use Astro.url to create new URLs by passing it as an argument to new URL().

src/pages/index.astro
---
// Example: Construct a canonical URL using your production domain
const canonicalURL = new URL(Astro.url.pathname, Astro.site);
// Example: Construct a URL for SEO meta tags using your current domain
const socialImageURL = new URL('/images/preview.png', Astro.url);
---
<link rel="canonical" href={canonicalURL} />
<meta property="og:image" content={socialImageURL} />

Astro.clientAddress

Section titled Astro.clientAddress

Type: string

Added in: astro@1.0.0-rc

Specifies the IP address of the request. This property is only available when building for SSR (server-side rendering) and should not be used for static sites.

---
const ip = Astro.clientAddress;
---


<div>Your IP address is: <span class="address">{ ip }</span></div>

Astro.site

Section titled Astro.site

Type: URL | undefined

Astro.site returns a URL made from site in your Astro config. If site in your Astro config isn’t defined, Astro.site won’t be defined.

Astro.generator

Section titled Astro.generator

Type: string

Added in: astro@1.0.0

Astro.generator is a convenient way to add a <meta name="generator"> tag with your current version of Astro. It follows the format "Astro v1.x.x".

<html>
  <head>
    <meta name="generator" content={Astro.generator} />
  </head>
  <body>
    <footer>
      <p>Built with <a href="https://astro.build">{Astro.generator}</a></p>
    </footer>
  </body>
</html>

Astro.slots

Section titled Astro.slots

Astro.slots contains utility functions for modifying an Astro component’s slotted children.

Astro.slots.has()

Section titled Astro.slots.has()

Type: (slotName: string) => boolean

You can check whether content for a specific slot name exists with Astro.slots.has(). This can be useful when you want to wrap slot contents, but only want to render the wrapper elements when the slot is being used.

src/pages/index.astro
---
---
<slot />


{Astro.slots.has('more') && (
  <aside>
    <h2>More</h2>
    <slot name="more" />
  </aside>
)}

Astro.slots.render()

Section titled Astro.slots.render()

Type: (slotName: string, args?: any[]) => Promise<string>

You can asynchronously render the contents of a slot to a string of HTML using Astro.slots.render().

---
const html = await Astro.slots.render('default');
---
<Fragment set:html={html} />

Astro.slots.render() optionally accepts a second argument: an array of parameters that will be forwarded to any function children. This can be useful for custom utility components.

For example, this <Shout /> component converts its message prop to uppercase and passes it to the default slot:

src/components/Shout.astro
---
const message = Astro.props.message.toUpperCase();
let html = '';
if (Astro.slots.has('default')) {
  html = await Astro.slots.render('default', [message]);
}
---
<Fragment set:html={html} />

A callback function passed as <Shout />’s child will receive the all-caps message parameter:

src/pages/index.astro
---
import Shout from "../components/Shout.astro";
---
<Shout message="slots!">
  {(message) => <div>{message}</div>}
</Shout>


<!-- renders as <div>SLOTS!</div> -->

Callback functions can be passed to named slots inside a wrapping HTML element tag with a slot attribute. This element is only used to transfer the callback to a named slot and will not be rendered onto the page.

<Shout message="slots!">
  <fragment slot="message">
    {(message) => <div>{message}</div>}
  </fragment>
</Shout>

Use a standard HTML element for the wrapping tag, or any lower case tag (e.g. <fragment> instead of <Fragment />) that will not be interpreted as a component. Do not use the HTML <slot> element as this will be interpreted as an Astro slot.

Astro.self

Section titled Astro.self

Astro.self allows Astro components to be recursively called. This behaviour lets you render an Astro component from within itself by using <Astro.self> in the component template. This can be helpful for iterating over large data stores and nested data-structures.

NestedList.astro
---
const { items } = Astro.props;
---
<ul class="nested-list">
  {items.map((item) => (
    <li>
      <!-- If there is a nested data-structure we render `<Astro.self>` -->
      <!-- and can pass props through with the recursive call -->
      {Array.isArray(item) ? (
        <Astro.self items={item} />
      ) : (
        item
      )}
    </li>
  ))}
</ul>

This component could then be used like this:

---
import NestedList from './NestedList.astro';
---
<NestedList items={['A', ['B', 'C'], 'D']} />

And would render HTML like this:

<ul class="nested-list">
  <li>A</li>
  <li>
    <ul class="nested-list">
      <li>B</li>
      <li>C</li>
    </ul>
  </li>
  <li>D</li>
</ul>

Astro.locals

Section titled Astro.locals

Added in: astro@2.4.0

Astro.locals is an object containing any values from the context.locals object from a middleware. Use this to access data returned by middleware in your .astro files.

src/pages/Orders.astro
---
const title = Astro.locals.welcomeTitle();
const orders = Array.from(Astro.locals.orders.entries());
---
<h1>{title}</h1>
<ul>
    {orders.map(order => {
        return <li>{/* do something with each order */}</li>
    })}
</ul>

Astro.preferredLocale

Section titled Astro.preferredLocale

Type: string | undefined

Added in: astro@3.5.0

Astro.preferredLocale is a computed value that represents the preferred locale of the user.

It is computed by checking the configured locales in your i18n.locales array and locales supported by the users’s browser via the header Accept-Language. This value is undefined if no such match exists.

This property is only available when building for SSR (server-side rendering) and should not be used for static sites.

Astro.preferredLocaleList

Section titled Astro.preferredLocaleList

Type: string[] | undefined

Added in: astro@3.5.0

Astro.preferredLocaleList represents the array of all locales that are both requested by the browser and supported by your website. This produces a list of all compatible languages between your site and your visitor.

If none of the browser’s requested languages are found in your locales array, then the value is []: you do not support any of your visitor’s preferred locales.

If the browser does not specify any preferred languages, then this value will be i18n.locales: all of your supported locales will be considered equally preferred by a visitor with no preferences.

This property is only available when building for SSR (server-side rendering) and should not be used for static sites.

Astro.currentLocale

Section titled Astro.currentLocale

Type: string | undefined

Added in: astro@3.5.6

The locale computed from the current URL, using the syntax specified in your locales configuration. If the URL does not contain a /[locale]/ prefix, then the value will default to i18n.defaultLocale.

Astro.getActionResult()

Section titled Astro.getActionResult()

Type: (action: TAction) => ActionReturnType<TAction> | undefined

Added in: astro@4.15.0

Astro.getActionResult() is a function that returns the result of an Action submission. This accepts an action function as an argument (e.g. actions.logout) and returns a data or error object when a submission is received. Otherwise, it will return undefined.

src/pages/index.astro
---
import { actions } from 'astro:actions';


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


<form action={actions.logout}>
  <button type="submit">Log out</button>
</form>
{result?.error && <p>Failed to log out. Please try again.</p>}

Astro.callAction()

Section titled Astro.callAction()

Added in: astro@4.15.0

Astro.callAction() is a function used to call an Action handler directly from your Astro component. This function accepts an Action function as the first argument (e.g. actions.logout) and any input that action receives as the second argument. It returns the result of the action as a promise.

src/pages/index.astro
---
import { actions } from 'astro:actions';


const { data, error } = await Astro.callAction(actions.logout, { userId: '123' });
---

Endpoint Context

Section titled Endpoint Context

Endpoint functions receive a context object as the first parameter. It mirrors many of the Astro global properties.

endpoint.json.ts
import type { APIContext } from 'astro';


export function GET(context: APIContext) {
  // ...
}

context.params

Section titled context.params

context.params is an object containing the values of dynamic route segments matched for this request.

In static builds, this will be the params returned by getStaticPaths() used for prerendering dynamic routes.

In SSR builds, this can be any value matching the path segments in the dynamic route pattern.

src/pages/posts/[id].json.ts
import type { APIContext } from 'astro';


export function getStaticPaths() {
  return [
    { params: { id: '1' } },
    { params: { id: '2' } },
    { params: { id: '3' } }
  ];
}


export function GET({ params }: APIContext) {
  return new Response(
    JSON.stringify({ id: params.id }),
  );
}

See also: params

context.props

Section titled context.props

Added in: astro@1.5.0

context.props is an object containing any props passed from getStaticPaths(). Because getStaticPaths() is not used when building for SSR (server-side rendering), context.props is only available in static builds.

src/pages/posts/[id].json.ts
import type { APIContext } from 'astro';


export function getStaticPaths() {
  return [
    { params: { id: '1' }, props: { author: 'Blu' } },
    { params: { id: '2' }, props: { author: 'Erika' } },
    { params: { id: '3' }, props: { author: 'Matthew' } }
  ];
}


export function GET({ props }: APIContext) {
  return new Response(
    JSON.stringify({ author: props.author }),
  );
}

See also: Data Passing with props

context.request

Section titled context.request

Type: Request

A standard Request object. It can be used to get the url, headers, method, and even body of the request.

import type { APIContext } from 'astro';


export function GET({ request }: APIContext) {
  return new Response(`Hello ${request.url}`);
}

See also: Astro.request

context.cookies

Section titled context.cookies

Type: AstroCookies

context.cookies contains utilities for reading and manipulating cookies.

See also: Astro.cookies

context.url

Section titled context.url

Type: URL

Added in: astro@1.5.0

A URL object constructed from the current context.request.url URL string value.

See also: Astro.url

context.clientAddress

Section titled context.clientAddress

Type: string

Added in: astro@1.5.0

Specifies the IP address of the request. This property is only available when building for SSR (server-side rendering) and should not be used for static sites.

import type { APIContext } from 'astro';


export function GET({ clientAddress }: APIContext) {
  return new Response(`Your IP address is: ${clientAddress}`);
}

See also: Astro.clientAddress

context.site

Section titled context.site

Type: URL | undefined

Added in: astro@1.5.0

context.site returns a URL made from site in your Astro config. If undefined, this will return a URL generated from localhost.

See also: Astro.site

context.generator

Section titled context.generator

Type: string

Added in: astro@1.5.0

context.generator is a convenient way to indicate the version of Astro your project is running. It follows the format "Astro v1.x.x".

src/pages/site-info.json.ts
import type { APIContext } from 'astro';


export function GET({ generator, site }: APIContext) {
  const body = JSON.stringify({ generator, site });
  return new Response(body);
}

See also: Astro.generator

context.redirect()

Section titled context.redirect()

Type: (path: string, status?: number) => Response

Added in: astro@1.5.0

context.redirect() returns a Response object that allows you to redirect to another page. This function is only available when building for SSR (server-side rendering) and should not be used for static sites.

import type { APIContext } from 'astro';


export function GET({ redirect }: APIContext) {
  return redirect('/login', 302);
}

See also: Astro.redirect()

context.rewrite()

Section titled context.rewrite()

Type: (rewritePayload: string | URL | Request) => Promise<Response>

Added in: astro@4.13.0

Allows you to serve content from a different URL or path without redirecting the browser to a new page.

The method accepts either a string, a URL, or a Request for the location of the path.

Use a string to provide an explicit path:

import type { APIContext } from 'astro';


export function GET({ rewrite }: APIContext) {
  return rewrite('/login');
}

Use a URL type when you need to construct the URL path for the rewrite. The following example renders a page’s parent path by creating a new URL from the relative "../" path:

import type { APIContext } from 'astro';


export function GET({ rewrite }: APIContext) {
  return rewrite(new URL("../", Astro.url));
}

Use a Request type for complete control of the Request sent to the server for the new path. The following example sends a request to render the parent page while also providing headers:

import type { APIContext } from 'astro';


export function GET({ rewrite }: APIContext) {
  return rewrite(new Request(new URL("../", Astro.url), {
   headers: {
     "x-custom-header": JSON.stringify(Astro.locals.someValue)
   }
 }));
}

See also: Astro.rewrite()

context.locals

Section titled context.locals

Added in: astro@2.4.0

context.locals is an object used to store and access arbitrary information during the lifecycle of a request.

Middleware functions can read and write the values of context.locals:

src/middleware.ts
import type { MiddlewareHandler } from 'astro';


export const onRequest: MiddlewareHandler = ({ locals }, next) => {
  if (!locals.title) {
    locals.title = "Default Title";
  }
  return next();
}

API endpoints can only read information from context.locals:

src/pages/hello.ts
import type { APIContext } from 'astro';


export function GET({ locals }: APIContext) {
  return new Response(locals.title); // "Default Title"
}

See also: Astro.locals

context.getActionResult()

Section titled context.getActionResult()

Type: (action: TAction) => ActionReturnType<TAction> | undefined

Added in: astro@4.15.0

context.getActionResult() is a function that returns the result of an Action submission. This accepts an action function as an argument (e.g. actions.logout), and returns a data or error object when a submission is received. Otherwise, it will return undefined.

See also Astro.getActionResult()

context.callAction()

Section titled context.callAction()

Added in: astro@4.15.0

context.callAction() is a function used to call an Action handler directly from your Astro component. This function accepts an Action function as the first argument (e.g. actions.logout) and any input that action receives as the second argument. It returns the result of the action as a promise.

See also Astro.callAction()

getStaticPaths()

Section titled getStaticPaths()

Type: (options: GetStaticPathsOptions) => Promise<GetStaticPathsResult> | GetStaticPathsResult

If a page uses dynamic params in the filename, that component will need to export a getStaticPaths() function.

This function is required because Astro is a static site builder. That means that your entire site is built ahead of time. If Astro doesn’t know to generate a page at build time, your users won’t see it when they visit your site.

---
export async function getStaticPaths() {
  return [
    { params: { /* required */ }, props: { /* optional */ } },
    { params: { ... } },
    { params: { ... } },
    // ...
  ];
}
---
<!-- Your HTML template here. -->

The getStaticPaths() function should return an array of objects to determine which paths will be pre-rendered by Astro.

It can also be used in static file endpoints for dynamic routing.

params

Section titled params

The params key of every returned object tells Astro what routes to build. The returned params must map back to the dynamic parameters and rest parameters defined in your component filepath.

params are encoded into the URL, so only strings are supported as values. The value for each params object must match the parameters used in the page name.

For example, suppose that you have a page at src/pages/posts/[id].astro. If you export getStaticPaths from this page and return the following for paths:

---
export async function getStaticPaths() {
  return [
    { params: { id: '1' } },
    { params: { id: '2' } },
    { params: { id: '3' } }
  ];
}


const { id } = Astro.params;
---
<h1>{id}</h1>

Then Astro will statically generate posts/1, posts/2, and posts/3 at build time.

Data Passing with props

Section titled Data Passing with props

To pass additional data to each generated page, you can also set a props value on every returned path object. Unlike params, props are not encoded into the URL and so aren’t limited to only strings.

For example, suppose that you generate pages based off of data fetched from a remote API. You can pass the full data object to the page component inside of getStaticPaths:

---
export async function getStaticPaths() {
  const data = await fetch('...').then(response => response.json());


  return data.map((post) => {
    return {
      params: { id: post.id },
      props: { post },
    };
  });
}


const { id } = Astro.params;
const { post } = Astro.props;
---
<h1>{id}: {post.name}</h1>

You can also pass a regular array, which may be helpful when generating or stubbing a known list of routes.

---
export async function getStaticPaths() {
  const posts = [
    {id: '1', category: "astro", title: "API Reference"},
    {id: '2', category: "react", title: "Creating a React Counter!"}
  ];
  return posts.map((post) => {
    return {
      params: { id: post.id },
      props: { post }
    };
  });
}
const {id} = Astro.params;
const {post} = Astro.props;
---
<body>
  <h1>{id}: {post.title}</h1>
  <h2>Category: {post.category}</h2>
</body>

Then Astro will statically generate posts/1 and posts/2 at build time using the page component in pages/posts/[id].astro. The page can reference this data using Astro.props:

paginate()

Section titled paginate()

Pagination is a common use-case for websites that Astro natively supports via the paginate() function. paginate() will automatically generate the array to return from getStaticPaths() that creates one URL for every page of the paginated collection. The page number will be passed as a param, and the page data will be passed as a page prop.

export async function getStaticPaths({ paginate }) {
  // Load your data with fetch(), Astro.glob(), etc.
  const response = await fetch(`https://pokeapi.co/api/v2/pokemon?limit=150`);
  const result = await response.json();
  const allPokemon = result.results;


  // Return a paginated collection of paths for all posts
  return paginate(allPokemon, { pageSize: 10 });
}


// If set up correctly, The page prop now has everything that
// you need to render a single page (see next section).
const { page } = Astro.props;

paginate() has the following arguments:

  • data - array containing the page’s data passed to the paginate() function
  • options - Optional object with the following properties:
    • pageSize - The number of items shown per page (10 by default)
    • params - Send additional parameters for creating dynamic routes
    • props - Send additional props to be available on each page

paginate() assumes a file name of [page].astro or [...page].astro. The page param becomes the page number in your URL:

  • /posts/[page].astro would generate the URLs /posts/1, /posts/2, /posts/3, etc.
  • /posts/[...page].astro would generate the URLs /posts, /posts/2, /posts/3, etc.

The pagination page prop

Section titled The pagination page prop

Type: Page<TData>

Pagination will pass a page prop to every rendered page that represents a single page of data in the paginated collection. This includes the data that you’ve paginated (page.data) as well as metadata for the page (page.url, page.start, page.end, page.total, etc). This metadata is useful for things like a “Next Page” button or a “Showing 1-10 of 100” message.

page.data
Section titled page.data

Type: Array<TData>

Array of data returned from the paginate() function for the current page.

page.start
Section titled page.start

Type: number

Index of first item on current page, starting at 0. (e.g. if pageSize: 25, this would be 0 on page 1, 25 on page 2, etc.)

page.end
Section titled page.end

Type: number

Index of last item on current page.

page.size
Section titled page.size

Type: number
Default: 10

How many items per-page.

page.total
Section titled page.total

Type: number

The total number of items across all pages.

page.currentPage
Section titled page.currentPage

Type: number

The current page number, starting with 1.

page.lastPage
Section titled page.lastPage

Type: number

The total number of pages.

page.url.current
Section titled page.url.current

Type: string

Get the URL of the current page (useful for canonical URLs).

page.url.prev
Section titled page.url.prev

Type: string | undefined

Get the URL of the previous page (will be undefined if on page 1). If a value is set for base, prepend the base path to the URL.

page.url.next
Section titled page.url.next

Type: string | undefined

Get the URL of the next page (will be undefined if no more pages). If a value is set for base, prepend the base path to the URL.

page.url.first
Section titled page.url.first

Type: string | undefined

Added in: astro@4.12.0

Get the URL of the first page (will be undefined if on page 1). If a value is set for base, prepend the base path to the URL.

page.url.last
Section titled page.url.last

Type: string | undefined

Added in: astro@4.12.0

Get the URL of the last page (will be undefined if no more pages). If a value is set for base, prepend the base path to the URL.

import.meta

Section titled import.meta

All ESM modules include a import.meta property. Astro adds import.meta.env through Vite.

import.meta.env.SSR can be used to know when rendering on the server. Sometimes you might want different logic, like a component that should only be rendered in the client:

export default function () {
  return import.meta.env.SSR ? <div class="spinner"></div> : <FancyComponent />;
}

Images (astro:assets)

Section titled Images (astro:assets)

getImage()

Section titled getImage()

Type: (options: UnresolvedImageTransform) => Promise<GetImageResult>

The getImage() function is intended for generating images destined to be used somewhere else than directly in HTML, for example in an API Route. It also allows you to create your own custom <Image /> component.

getImage() takes an options object with the same properties as the Image component (except alt).

---
import { getImage } from "astro:assets";
import myBackground from "../background.png"


const optimizedBackground = await getImage({src: myBackground, format: 'avif'})
---


<div style={`background-image: url(${optimizedBackground.src});`}></div>

It returns an object with the following type:

type GetImageResult = {
  /* Additional HTML attributes needed to render the image (width, height, style, etc..) */
  attributes: Record<string, any>;
  /* Validated parameters passed */
  options: ImageTransform;
  /* Original parameters passed */
  rawOptions: ImageTransform;
  /* Path to the generated image */
  src: string;
  srcSet: {
    /* Generated values for srcset, every entry has a url and a size descriptor */
    values: SrcSetValue[];
    /* A value ready to use in`srcset` attribute */
    attribute: string;
  };
}

Content Collections (astro:content)

Section titled Content Collections (astro:content)

Added in: astro@2.0.0

Content collections offer APIs to configure and query your Markdown or MDX documents in src/content/. For features and usage examples, see our content collections guide.

defineCollection()

Section titled defineCollection()

Type: (input: CollectionConfig) => CollectionConfig

defineCollection() is a utility to configure a collection in a src/content/config.* file.

src/content/config.ts
import { z, defineCollection } from 'astro:content';
const blog = defineCollection({
  type: 'content',
  schema: z.object({
    title: z.string(),
    permalink: z.string().optional(),
  }),
});


// Expose your defined collection to Astro
// with the `collections` export
export const collections = { blog };

This function accepts the following properties:

type

Section titled type

Type: 'content' | 'data'
Default: 'content'

Added in: astro@2.5.0

type is a string that defines the type of entries stored within a collection:

  • 'content' - for content-authoring formats like Markdown (.md), MDX (.mdx), or Markdoc (.mdoc)
  • 'data' - for data-only formats like JSON (.json) or YAML (.yaml)

schema

Section titled schema

Type: ZodType | (context: SchemaContext) => ZodType

schema is an optional Zod object to configure the type and shape of document frontmatter for a collection. Each value must use a Zod validator.

See the Content Collection guide for example usage.

reference()

Section titled reference()

Type: (collection: string) => ZodEffects<ZodString, { collection, id: string } | { collection, slug: string }>

Added in: astro@2.5.0

The reference() function is used in the content config to define a relationship, or “reference,” from one collection to another. This accepts a collection name and validates the entry identifier(s) specified in your content frontmatter or data file.

This example defines references from a blog author to the authors collection and an array of related posts to the same blog collection:

import { defineCollection, reference, z } from 'astro:content';


const blog = defineCollection({
  type: 'content',
  schema: z.object({
    // Reference a single author from the `authors` collection by `id`
    author: reference('authors'),
    // Reference an array of related posts from the `blog` collection by `slug`
    relatedPosts: z.array(reference('blog')),
  })
});


const authors = defineCollection({
  type: 'data',
  schema: z.object({ /* ... */ })
});


export const collections = { blog, authors };

See the Content Collection guide for example usage.

getCollection()

Section titled getCollection()

Type: (collection: string, filter?: (entry: CollectionEntry<TCollectionName>) => boolean) => CollectionEntry<TCollectionName>[]

getCollection() is a function that retrieves a list of content collection entries by collection name.

It returns all items in the collection by default, and accepts an optional filter function to narrow by entry properties. This allows you to query for only some items in a collection based on id, slug, or frontmatter values via the data object.

---
import { getCollection } from 'astro:content';


// Get all `src/content/blog/` entries
const allBlogPosts = await getCollection('blog');


// Only return posts with `draft: true` in the frontmatter
const draftBlogPosts = await getCollection('blog', ({ data }) => {
  return data.draft === true;
});
---

See the Content Collection guide for example usage.

getEntry()

Section titled getEntry()

Added in: astro@2.5.0

Types:

  • (collection: string, contentSlugOrDataId: string) => CollectionEntry<TCollectionName>
  • ({ collection: string, id: string }) => CollectionEntry<TCollectionName>
  • ({ collection: string, slug: string }) => CollectionEntry<TCollectionName>

getEntry() is a function that retrieves a single collection entry by collection name and either the entry id (for type: 'data' collections) or entry slug (for type: 'content' collections). getEntry() can also be used to get referenced entries to access the data, body, or render() properties:

---
import { getEntry } from 'astro:content';


// Get `src/content/blog/enterprise.md`
const enterprisePost = await getEntry('blog', 'enterprise');


// Get `src/content/captains/picard.yaml`
const picardProfile = await getEntry('captains', 'picard');


// Get the profile referenced by `data.captain`
const enterpriseCaptainProfile = await getEntry(enterprisePost.data.captain);
---

See the Content Collections guide for examples of querying collection entries.

getEntries()

Section titled getEntries()

Added in: astro@2.5.0

Types:

  • (Array<{ collection: string, id: string }>) => CollectionEntry<TCollectionName>[]
  • (Array<{ collection: string, slug: string }>) => CollectionEntry<TCollectionName>[]

getEntries() is a function that retrieves multiple collection entries from the same collection. This is useful for returning an array of referenced entries to access their associated data, body, and render() properties.

---
import { getEntries } from 'astro:content';


const enterprisePost = await getEntry('blog', 'enterprise');


// Get related posts referenced by `data.relatedPosts`
const enterpriseRelatedPosts = await getEntries(enterprisePost.data.relatedPosts);
---

getEntryBySlug()

Section titled getEntryBySlug()

Type: (collection: string, slug: string) => Promise<CollectionEntry<TCollectionName>>

getEntryBySlug() is a function that retrieves a single collection entry by collection name and entry slug.

---
import { getEntryBySlug } from 'astro:content';


const enterprise = await getEntryBySlug('blog', 'enterprise');
---

See the Content Collection guide for example usage.

getDataEntryById()

Section titled getDataEntryById()

Type: (collection: string, id: string) => Promise<CollectionEntry<TCollectionName>>

Added in: astro@2.5.0

getDataEntryById() is a function that retrieves a single collection entry by collection name and entry id.

---
import { getDataEntryById } from 'astro:content';


const picardProfile = await getDataEntryById('captains', 'picard');
---

Collection Entry Type

Section titled Collection Entry Type

Query functions including getCollection(), getEntry(), and getEntries() each return entries with the CollectionEntry type. This type is available as a utility from astro:content:

import type { CollectionEntry } from 'astro:content';

The CollectionEntry<TCollectionName> type is an object with the following values. TCollectionName is the name of the collection you’re querying (e.g. CollectionEntry<'blog'>).

id

Section titled id

Available for: type: 'content' and type: 'data' collections
Example Types:

  • content collections: 'entry-1.md' | 'entry-2.md' | ...
  • data collections: 'author-1' | 'author-2' | ...

A unique ID using the file path relative to src/content/[collection]. Enumerates all possible string values based on the collection entry file paths. Note that collections defined as type: 'content' include the file extension in their ID, while collections defined as type: 'data' do not.

collection

Section titled collection

Available for: type: 'content' and type: 'data' collections
Example Type: 'blog' | 'authors' | ...

The name of a top-level folder under src/content/ in which entries are located. This is the name used to reference the collection in your schema, and in querying functions.

data

Section titled data

Available for: type: 'content' and type: 'data' collections
Type: CollectionSchema<TCollectionName>

An object of frontmatter properties inferred from your collection schema (see defineCollection() reference). Defaults to any if no schema is configured.

slug

Section titled slug

Available for: type: 'content' collections only
Example Type: 'entry-1' | 'entry-2' | ...

A URL-ready slug for Markdown or MDX documents. Defaults to the id without the file extension, but can be overridden by setting the slug property in a file’s frontmatter.

body

Section titled body

Available for: type: 'content' collections only
Type: string

A string containing the raw, uncompiled body of the Markdown or MDX document.

render()

Section titled render()

Available for: type: 'content' collections only
Type: () => Promise<RenderedEntry>

A function to compile a given Markdown or MDX document for rendering. This returns the following properties:

---
import { getEntryBySlug } from 'astro:content';
const entry = await getEntryBySlug('blog', 'entry-1');


const { Content, headings, remarkPluginFrontmatter } = await entry.render();
---

See the Content Collection guide for example usage.

Other Content Collection Types

Section titled Other Content Collection Types

The astro:content module also exports the following types for use in your Astro project:

CollectionKey

Section titled CollectionKey

Added in: astro@3.1.0

A string union of all collection names defined in your src/content/config.* file. This type can be useful when defining a generic function that accepts any collection name.

import type { CollectionKey, getCollection } from 'astro:content';


async function getCollection(collection: CollectionKey) {
  return getCollection(collection);
}

ContentCollectionKey

Section titled ContentCollectionKey

Added in: astro@3.1.0

A string union of all the names of type: 'content' collections defined in your src/content/config.* file.

DataCollectionKey

Section titled DataCollectionKey

Added in: astro@3.1.0

A string union of all the names of type: 'data' collection defined in your src/content/config.* file.

SchemaContext

Section titled SchemaContext

The context object that defineCollection uses for the function shape of schema. This type can be useful when building reusable schemas for multiple collections.

This includes the following property:

import type { SchemaContext } from 'astro:content';


export const imageSchema = ({ image }: SchemaContext) =>
    z.object({
        image: image(),
        description: z.string().optional(),
    });


const blog = defineCollection({
  type: 'content',
  schema: ({ image }) => z.object({
    title: z.string(),
    permalink: z.string().optional(),
    image: imageSchema({ image })
  }),
});

Middleware (astro:middleware)

Section titled Middleware (astro:middleware)

Added in: astro@2.6.0

Middleware allows you to intercept requests and responses and inject behaviors dynamically every time a page or endpoint is about to be rendered. For features and usage examples, see our middleware guide.

onRequest()

Section titled onRequest()

Type: (context: APIContext, next: MiddlewareNext) => Promise<Response> | Response | Promise<void> | void

A required exported function from src/middleware.js that will be called before rendering every page or API route. It receives two arguments: context and next(). onRequest() must return a Response: either directly, or by calling next().

src/middleware.js
export function onRequest (context, next) {
    // intercept response data from a request
    // optionally, transform the response
    // return a Response directly, or the result of calling `next()`
    return next();
};

context

Section titled context

Type: APIContext

The first argument of onRequest() is a context object. It mirrors many of the Astro global properties.

See Endpoint contexts for more information about the context object.

next()

Section titled next()

Type: (rewritePayload?: string | URL | Request) => Promise<Response>

The second argument of onRequest() is a function that calls all the subsequent middleware in the chain and returns a Response. For example, other middleware could modify the HTML body of a response and awaiting the result of next() would allow your middleware to respond to those changes.

Since Astro v4.13.0, next() accepts an optional URL path parameter in the form of a string, URL, or Request to rewrite the current request without retriggering a new rendering phase.

sequence()

Section titled sequence()

Type: (...handlers: MiddlewareHandler[]) => MiddlewareHandler

A function that accepts middleware functions as arguments, and will execute them in the order in which they are passed.

src/middleware.js
import { sequence } from "astro:middleware";


async function validation(_, next) {...}
async function auth(_, next) {...}
async function greeting(_, next) {...}


export const onRequest = sequence(validation, auth, greeting);

createContext()

Section titled createContext()

Type: (context: CreateContext) => APIContext

Added in: astro@2.8.0

A low-level API to create an APIContextto be passed to an Astro middleware onRequest() function.

This function can be used by integrations/adapters to programmatically execute the Astro middleware.

trySerializeLocals()

Section titled trySerializeLocals()

Type: (value: unknown) => string

Added in: astro@2.8.0

A low-level API that takes in any value and tries to return a serialized version (a string) of it. If the value cannot be serialized, the function will throw a runtime error.

Internationalization (astro:i18n)

Section titled Internationalization (astro:i18n)

Added in: astro@3.5.0

This module provides functions to help you create URLs using your project’s configured locales.

Creating routes for your project with the i18n router will depend on certain configuration values you have set that affect your page routes. When creating routes with these functions, be sure to take into account your individual settings for:

Also, note that the returned URLs created by these functions for your defaultLocale will reflect your i18n.routing configuration.

For features and usage examples, see our i18n routing guide.

getRelativeLocaleUrl()

Section titled getRelativeLocaleUrl()

Type: (locale: string, path?: string, options?: GetLocaleOptions) => string

Use this function to retrieve a relative path for a locale. If the locale doesn’t exist, Astro throws an error.

---
getRelativeLocaleUrl("fr");
// returns /fr


getRelativeLocaleUrl("fr", "");
// returns /fr


getRelativeLocaleUrl("fr", "getting-started");
// returns /fr/getting-started


getRelativeLocaleUrl("fr_CA", "getting-started", {
  prependWith: "blog"
});
// returns /blog/fr-ca/getting-started


getRelativeLocaleUrl("fr_CA", "getting-started", {
  prependWith: "blog",
  normalizeLocale: false
});
// returns /blog/fr_CA/getting-started
---

getAbsoluteLocaleUrl()

Section titled getAbsoluteLocaleUrl()

Type: (locale: string, path: string, options?: GetLocaleOptions) => string

Use this function to retrieve an absolute path for a locale when [site] has a value. If [site] isn’t configured, the function returns a relative URL. If the locale doesn’t exist, Astro throws an error.

src/pages/index.astro
---
// If `site` is set to be `https://example.com`


getAbsoluteLocaleUrl("fr");
// returns https://example.com/fr


getAbsoluteLocaleUrl("fr", "");
// returns https://example.com/fr


getAbsoluteLocaleUrl("fr", "getting-started");
// returns https://example.com/fr/getting-started


getAbsoluteLocaleUrl("fr_CA", "getting-started", {
  prependWith: "blog"
});
// returns https://example.com/blog/fr-ca/getting-started


getAbsoluteLocaleUrl("fr_CA", "getting-started", {
  prependWith: "blog",
  normalizeLocale: false
});
// returns https://example.com/blog/fr_CA/getting-started
---

getRelativeLocaleUrlList()

Section titled getRelativeLocaleUrlList()

Type: (path?: string, options?: GetLocaleOptions) => string[]

Use this like getRelativeLocaleUrl to return a list of relative paths for all the locales.

getAbsoluteLocaleUrlList()

Section titled getAbsoluteLocaleUrlList()

Type: (path?: string, options?: GetLocaleOptions) => string[]

Use this like getAbsoluteLocaleUrl to return a list of absolute paths for all the locales.

getPathByLocale()

Section titled getPathByLocale()

Type: (locale: string) => string

A function that returns the path associated to one or more codes when custom locale paths are configured.

astro.config.mjs
export default defineConfig({
  i18n: {
    locales: ["es", "en", {
      path: "french",
      codes: ["fr", "fr-BR", "fr-CA"]
    }]
  }
})
src/pages/index.astro
---
getPathByLocale("fr"); // returns "french"
getPathByLocale("fr-CA"); // returns "french"
---

getLocaleByPath()

Section titled getLocaleByPath()

Type: (path: string) => string

A function that returns the code associated to a locale path.

astro.config.mjs
export default defineConfig({
  i18n: {
    locales: ["es", "en", {
      path: "french",
      codes: ["fr", "fr-BR", "fr-CA"]
    }]
  }
})
src/pages/index.astro
---
getLocaleByPath("french"); // returns "fr" because that's the first code configured
---

redirectToDefaultLocale()

Section titled redirectToDefaultLocale()

Type: (context: APIContext, statusCode?: ValidRedirectStatus) => Promise<Response>

Added in: astro@4.6.0

A function that returns a Response that redirects to the defaultLocale configured. It accepts an optional valid redirect status code.

middleware.js
import { defineMiddleware } from "astro:middleware";
import { redirectToDefaultLocale } from "astro:i18n";


export const onRequest = defineMiddleware((context, next) => {
  if (context.url.pathname.startsWith("/about")) {
    return next();
  } else {
    return redirectToDefaultLocale(context, 302);
  }
})

redirectToFallback()

Section titled redirectToFallback()

Type: (context: APIContext, response: Response) => Promise<Response>

Added in: astro@4.6.0

A function that allows you to use your i18n.fallback configuration in your own middleware.

middleware.js
import { defineMiddleware } from "astro:middleware";
import { redirectToFallback } from "astro:i18n";


export const onRequest = defineMiddleware(async (context, next) => {
  const response = await next();
  if (response.status >= 300) {
    return redirectToFallback(context, response)
  }
  return response;
})

notFound()

Section titled notFound()

Type: (context: APIContext, response?: Response) => Promise<Response> | undefined

Added in: astro@4.6.0

Use this function in your routing middleware to return a 404 when:

  • the current path isn’t a root. e.g. / or /<base>
  • the URL doesn’t contain a locale

When a Response is passed, the new Response emitted by this function will contain the same headers of the original response.

middleware.js
import { defineMiddleware } from "astro:middleware";
import { notFound } from "astro:i18n";


export const onRequest = defineMiddleware((context, next) => {
  const pathNotFound = notFound(context);
  if (pathNotFound) {
    return pathNotFound;
  }
  return next();
})

middleware()

Section titled middleware()

Type: (options: { prefixDefaultLocale: boolean, redirectToDefaultLocale: boolean }) => MiddlewareHandler

Added in: astro@4.6.0

A function that allows you to programmatically create the Astro i18n middleware.

This is use useful when you still want to use the default i18n logic, but add only a few exceptions to your website.

middleware.js
import { middleware } from "astro:i18n";
import { sequence, defineMiddleware } from "astro:middleware";


const customLogic = defineMiddleware(async (context, next) => {
  const response = await next();


  // Custom logic after resolving the response.
  // It's possible to catch the response coming from Astro i18n middleware.


  return response;
});


export const onRequest = sequence(customLogic, middleware({
  prefixDefaultLocale: true,
  redirectToDefaultLocale: false
}))

requestHasLocale()

Section titled requestHasLocale()

Type: (context: APIContext) => boolean

Added in: astro@4.6.0

Checks whether the current URL contains a configured locale. Internally, this function will use APIContext#url.pathname.

middleware.js
import { defineMiddleware } from "astro:middleware";
import { requestHasLocale } from "astro:i18n";


export const onRequest = defineMiddleware(async (context, next) => {
  if (requestHasLocale(context)) {
    return next();
  }
  return new Response("Not found", { status: 404 });
})

View Transitions client API (astro:transitions/client)

Section titled View Transitions client API (astro:transitions/client)

Added in: astro@3.2.0

This module provides functions to control and interact with the View Transitions API and client-side router.

For features and usage examples, see our View Transitions guide.

Section titled navigate()

Type: (href: string, options?: Options) => void

Added in: astro@3.2.0

A function that executes a navigation to the given href using the View Transitions API.

This function signature is based on the navigate function from the browser Navigation API. Although based on the Navigation API, this function is implemented on top of the History API to allow for navigation without reloading the page.

history option

Section titled history option

Type: 'auto' | 'push' | 'replace'
Default: 'auto'

Added in: astro@3.2.0

Defines how this navigation should be added to the browser history.

  • 'push': the router will use history.pushState to create a new entry in the browser history.
  • 'replace': the router will use history.replaceState to update the URL without adding a new entry into navigation.
  • 'auto' (default): the router will attempt history.pushState, but if the URL cannot be transitioned to, the current URL will remain with no changes to the browser history.

This option follows the history option from the browser Navigation API but simplified for the cases that can happen on an Astro project.

formData option

Section titled formData option

Type: FormData

Added in: astro@3.5.0

A FormData object for POST requests.

When this option is provided, the requests to the navigation target page will be sent as a POST request with the form data object as the content.

Submitting an HTML form with view transitions enabled will use this method instead of the default navigation with page reload. Calling this method allows triggering the same behavior programmatically.

info option

Section titled info option

Type: any

Added in: astro@3.6.0

Arbitrary data to be included in the astro:before-preparation and astro:before-swap events caused by this navigation.

This option mimics the info option from the browser Navigation API.

state option

Section titled state option

Type: any

Added in: astro@3.6.0

Arbitrary data to be associated with the NavitationHistoryEntry object created by this navigation. This data can then be retrieved using the history.getState function from the History API.

This option mimics the state option from the browser Navigation API.

sourceElement option

Section titled sourceElement option

Type: Element

Added in: astro@3.6.0

The element that triggered this navigation, if any. This element will be available in the following events:

  • astro:before-preparation
  • astro:before-swap

supportsViewTransitions

Section titled supportsViewTransitions

Type: boolean

Added in: astro@3.2.0

Whether or not view transitions are supported and enabled in the current browser.

transitionEnabledOnThisPage

Section titled transitionEnabledOnThisPage

Type: boolean

Added in: astro@3.2.0

Whether or not the current page has view transitions enabled for client-side navigation. This can be used to make components that behave differently when they are used on pages with view transitions.

getFallback

Section titled getFallback

Type: () => 'none' | 'animate' | 'swap'

Added in: astro@3.6.0

Returns the fallback strategy to use in browsers that do not support view transitions.

See the guide on Fallback control for how to choose and configure the fallback behavior.

astro:before-preparation event

Section titled astro:before-preparation event

An event dispatched at the beginning of a navigation using View Transitions. This event happens before any request is made and any browser state is changed.

This event has the attributes:

Read more about how to use this event on the View Transitions guide.

astro:after-preparation event

Section titled astro:after-preparation event

An event dispatched after the next page in a navigation using View Transitions is loaded.

This event has no attributes.

Read more about how to use this event on the View Transitions guide.

astro:before-swap event

Section titled astro:before-swap event

An event dispatched after the next page is parsed, prepared, and linked into a document in preparation for the transition but before any content is swapped between the documents.

This event can’t be canceled. Calling preventDefault() is a no-op.

This event has the attributes:

Read more about how to use this event on the View Transitions guide.

astro:after-swap event

Section titled astro:after-swap event

An event dispatched after the contents of the page have been swapped but before the view transition ends.

The history entry and scroll position have already been updated when this event is triggered.

astro:page-load event

Section titled astro:page-load event

An event dispatched after a page completes loading, whether from a navigation using view transitions or native to the browser.

When view transitions is enabled on the page, code that would normally execute on DOMContentLoaded should be changed to execute on this event.

View Transitions events attributes

Section titled View Transitions events attributes

Added in: astro@3.6.0

info

Section titled info

Type: URL

Arbitrary data defined during navigation.

This is the literal value passed on the info option of the navigate() function.

sourceElement

Section titled sourceElement

Type: Element | undefined

The element that triggered the navigation. This can be, for example, an <a> element that was clicked.

When using the navigate() function, this will be the element specified in the call.

newDocument

Section titled newDocument

Type: Document

The document for the next page in the navigation. The contents of this document will be swapped in place of the contents of the current document.

Section titled navigationType

Type: 'push' | 'replace' | 'traverse'

Which kind of history navigation is happening.

  • push: a new NavigationHistoryEntry is being created for the new page.
  • replace: the current NavigationHistoryEntry is being replaced with an entry for the new page.
  • traverse: no NavigationHistoryEntry is created. The position in the history is changing. The direction of the traversal is given on the direction attribute

direction

Section titled direction

Type: Direction

The direction of the transition.

  • forward: navigating to the next page in the history or to a new page.
  • back: navigating to the previous page in the history.
  • Anything else some other listener might have set.

from

Section titled from

Type: URL

The URL of the page initiating the navigation.

to

Section titled to

Type: URL

The URL of the page being navigated to. This property can be modified, the value at the end of the lifecycle will be used in the NavigationHistoryEntry for the next page.

formData

Section titled formData

Type: FormData | undefined

A FormData object for POST requests.

When this attribute is set, a POST request will be sent to the to URL with the given form data object as the content instead of the normal GET request.

When submitting an HTML form with view transitions enabled, this field is automatically set to the data in the form. When using the navigate() function, this value is the same as given in the options.

loader

Section titled loader

Type: () => Promise<void>

Implementation of the following phase in the navigation (loading the next page). This implementation can be overridden to add extra behavior.

viewTransition

Section titled viewTransition

Type: ViewTransition

The view transition object used in this navigation. On browsers that do not support the View Transitions API, this is an object implementing the same API for convenience but without the DOM integration.

swap

Section titled swap

Type: () => void

Implementation of the document swap logic.

Read more on how to build your own custom swap function on the View Transitions guide.

By default, this implementation will call the following functions in order:

deselectScripts()
Section titled deselectScripts()

Type: (newDocument: Document) => void

Marks scripts in the new document that should not be executed. Those scripts are already in the current document and are not flagged for re-execution using data-astro-rerun.

swapRootAttributes()
Section titled swapRootAttributes()

Type: (newDocument: Document) => void

Swaps the attributes between the document roots, like the lang attribute. This also includes Astro-injected internal attributes like data-astro-transition, which makes the transition direction available to Astro-generated CSS rules.

When making a custom swap function, it is important to call this function so as not to break the view transition’s animations.

swapHeadElements()
Section titled swapHeadElements()

Type: (newDocument: Document) => void

Removes every element from the current document’s <head> that is not persisted to the new document. Then appends all new elements from the new document’s <head> to the current document’s <head>.

saveFocus()
Section titled saveFocus()

Type: () => () => void

Stores the element in focus on the current page and returns a function that when called, if the focused element was persisted, returns the focus to it.

swapBodyElements()
Section titled swapBodyElements()

Type: (newBody: Element, oldBody: Element) => void

Replaces the old body with the new body. Then, goes through every element in the old body that should be persisted and have a matching element in the new body and swaps the old element back in place.

Actions (astro:actions)

Section titled Actions (astro:actions)

Added in: astro@4.15.0

Actions help you build a type-safe backend you can call from client code and HTML forms. All utilities to define and call actions are exposed by the astro:actions module. For examples and usage instructions, see the Actions guide.

defineAction()

Section titled defineAction()

Added in: astro@4.15.0

The defineAction() utility is used to define new actions from the src/actions/index.ts file. This accepts a handler() function containing the server logic to run, and an optional input property to validate input parameters at runtime.

export const server = {
  getGreeting: defineAction({
    input: z.object({
      name: z.string(),
    }),
    handler: async (input, context) => {
      return `Hello, ${input.name}!`
    }
  })
}

handler() property

Section titled handler() property

Type: (input, context) => any

defineAction() requires a handler() function containing the server logic to run when the action is called. Data returned from the handler is automatically serialized and sent to the caller.

The handler() is called with user input as its first argument. If an input validator is set, the user input will be validated before being passed to the handler. The second argument is a context object containing most of Astro’s standard endpoint context, excluding getActionResult(), callAction(), and redirect().

Return values are parsed using the devalue library. This supports JSON values and instances of Date(), Map(), Set(), and URL().

input validator

Section titled input validator

Type: ZodType | undefined

The optional input property accepts a Zod validator to validate handler inputs at runtime. If the action fails to validate, a BAD_REQUEST error is returned and the handler is not called.

If input is omitted, the handler will receive an input of type unknown for JSON requests and type FormData for form requests.

Use with accept: 'form'
Section titled Use with accept: &#39;form&#39;

If your action accepts form inputs, use the z.object() validator to automatically parse form data to a typed object. The following validators are supported for form data fields:

  • Inputs of type number can be validated using z.number()
  • Inputs of type checkbox can be validated using z.boolean()
  • Inputs of type file can be validated using z.instanceof(File)
  • Multiple inputs of the same name can be validated using z.array(/* validator */)
  • All other inputs can be validated using z.string()

Extension functions including .refine(), .transform(), and .pipe() are also supported on the z.object() validator.

To apply a union of different validators, use the z.discriminatedUnion() wrapper to narrow the type based on a specific form field. This example accepts a form submission to either “create” or “update” a user, using the form field with the name type to determine which object to validate against:

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


export const server = {
  changeUser: defineAction({
    accept: 'form',
    input: z.discriminatedUnion('type', [
      z.object({
        // Matches when the `type` field has the value `create`
        type: z.literal('create'),
        name: z.string(),
        email: z.string().email(),
      }),
      z.object({
        // Matches when the `type` field has the value `update`
        type: z.literal('update'),
        id: z.number(),
        name: z.string(),
        email: z.string().email(),
      }),
    ]),
    async handler(input) {
      if (input.type === 'create') {
        // input is { type: 'create', name: string, email: string }
      } else {
        // input is { type: 'update', id: number, name: string, email: string }
      }
    },
  }),
};

isInputError()

Section titled isInputError()

Type: (error?: unknown | ActionError) => boolean

Added in: astro@4.15.0

The isInputError() utility is used to check whether an ActionError is an input validation error. When the input validator is a z.object(), input errors include a fields object with error messages grouped by name.

See the form input errors guide for more on using isInputError().

ActionError

Section titled ActionError

Added in: astro@4.15.0

The ActionError() constructor is used to create errors thrown by an action handler. This accepts a code property describing the error that occurred (example: "UNAUTHORIZED"), and an optional message property with further details.

code

Section titled code

Added in: astro@4.15.0

The code property accepts human-readable versions of all HTTP status codes. The following codes are supported:

  • BAD_REQUEST (400): The client sent invalid input. This error is thrown when an action input validator fails to validate.
  • UNAUTHORIZED (401): The client lacks valid authentication credentials.
  • FORBIDDEN (403): The client is not authorized to access a resource.
  • NOT_FOUND (404): The server cannot find the requested resource.
  • METHOD_NOT_SUPPORTED (405): The server does not support the requested method.
  • TIMEOUT (408): The server timed out while processing the request.
  • CONFLICT (409): The server cannot update a resource due to a conflict.
  • PRECONDITION_FAILED (412): The server does not meet a precondition of the request.
  • PAYLOAD_TOO_LARGE (413): The server cannot process the request because the payload is too large.
  • UNSUPPORTED_MEDIA_TYPE (415): The server does not support the request’s media type. Note: Actions already check the Content-Type header for JSON and form requests, so you likely won’t need to raise this code manually.
  • UNPROCESSABLE_CONTENT (422): The server cannot process the request due to semantic errors.
  • TOO_MANY_REQUESTS (429): The server has exceeded a specified rate limit.
  • CLIENT_CLOSED_REQUEST (499): The client closed the request before the server could respond.
  • INTERNAL_SERVER_ERROR (500): The server failed unexpectedly.
  • NOT_IMPLEMENTED (501): The server does not support the requested feature.
  • BAD_GATEWAY (502): The server received an invalid response from an upstream server.
  • SERVICE_UNAVAILABLE (503): The server is temporarily unavailable.
  • GATEWAY_TIMEOUT (504): The server received a timeout from an upstream server.

message

Section titled message

Added in: astro@4.15.0

The message property accepts a string. (e.g. “User must be logged in.“)

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