Remote functions

Available since SvelteKit 2.27. This feature is experimental and subject to change without notice.

Remote functions are a tool for type-safe communication between client and server. They can be called anywhere in your app, but always run on the server, meaning they can safely access server-only modules containing things like environment variables and database clients.

Enabling remote functions

You must opt in by adding the kit.experimental.remoteFunctions option in your svelte.config.js:

/// file: svelte.config.js
/** @type {import('@sveltejs/kit').Config} */
const config = {
	kit: {
		experimental: {
			remoteFunctions: true
		}
	},
	compilerOptions: {
		experimental: {
			async: true  // Optional: enables await in components
		}
	}
};

export default config;

Overview

Remote functions are exported from a .remote.js or .remote.ts file and come in four flavors:

query

Read dynamic data from the server

form

Submit form data with progressive enhancement

command

Write data to the server from anywhere

prerender

Prerender static data at build time

On the client, exported functions are transformed to fetch wrappers that invoke their counterparts on the server via a generated HTTP endpoint.

query

The query function allows you to read dynamic data from the server:

/// file: src/routes/blog/data.remote.js
import { query } from '$app/server';
import * as db from '$lib/server/database';

export const getPosts = query(async () => {
	const posts = await db.sql`
		SELECT title, slug
		FROM post
		ORDER BY published_at DESC
	`;

	return posts;
});

Until the promise resolves — and if it errors — the nearest <svelte:boundary> will be invoked.

Query arguments

Query functions can accept an argument. Use a Standard Schema validation library like Zod or Valibot to validate:

/// file: src/routes/blog/data.remote.js
import * as v from 'valibot';
import { error } from '@sveltejs/kit';
import { query } from '$app/server';
import * as db from '$lib/server/database';

export const getPost = query(v.string(), async (slug) => {
	const [post] = await db.sql`
		SELECT * FROM post
		WHERE slug = ${slug}
	`;

	if (!post) error(404, 'Not found');
	return post;
});

Use it in your component:

<!--- file: src/routes/blog/[slug]/+page.svelte --->
<script>
	import { getPost } from '../data.remote';

	let { params } = $props();

	const post = $derived(await getPost(params.slug));
</script>

<h1>{post.title}</h1>
<div>{@html post.content}</div>

Refreshing queries

Any query can be re-fetched via its refresh method:

<button onclick={() => getPosts().refresh()}>
	Check for new posts
</button>

Queries are cached while they’re on the page, meaning getPosts() === getPosts(). You don’t need a reference to update the query.

query.batch

query.batch batches requests that happen within the same macrotask, solving the n+1 problem:

/// file: weather.remote.js
import * as v from 'valibot';
import { query } from '$app/server';
import * as db from '$lib/server/database';

export const getWeather = query.batch(v.string(), async (cityIds) => {
	const weather = await db.sql`
		SELECT * FROM weather
		WHERE city_id = ANY(${cityIds})
	`;
	const lookup = new Map(weather.map(w => [w.city_id, w]));

	return (cityId) => lookup.get(cityId);
});

Use it in your component:

<!--- file: Weather.svelte --->
<script>
	import CityWeather from './CityWeather.svelte';
	import { getWeather } from './weather.remote';

	let { cities } = $props();
	let limit = $state(5);
</script>

<h2>Weather</h2>

{#each cities.slice(0, limit) as city}
	<h3>{city.name}</h3>
	<CityWeather weather={await getWeather(city.id)} />
{/each}

{#if cities.length > limit}
	<button onclick={() => limit += 5}>
		Load more
	</button>
{/if}

form

The form function makes it easy to write data to the server:

/// file: src/routes/blog/data.remote.js
import * as v from 'valibot';
import { error, redirect } from '@sveltejs/kit';
import { form } from '$app/server';
import * as db from '$lib/server/database';
import * as auth from '$lib/server/auth';

export const createPost = form(
	v.object({
		title: v.pipe(v.string(), v.nonEmpty()),
		content: v.pipe(v.string(), v.nonEmpty())
	}),
	async ({ title, content }) => {
		const user = await auth.getUser();
		if (!user) error(401, 'Unauthorized');

		const slug = title.toLowerCase().replace(/ /g, '-');

		await db.sql`
			INSERT INTO post (slug, title, content)
			VALUES (${slug}, ${title}, ${content})
		`;

		redirect(303, `/blog/${slug}`);
	}
);

The form object contains method and action properties that allow it to work without JavaScript. It also has an attachment that progressively enhances the form when JavaScript is available.

Fields

A form is composed of fields defined by the schema. To get attributes for a field, call its .as(...) method:

<form {...createPost}>
	<label>
		<h2>Title</h2>
		<input {...createPost.fields.title.as('text')} />
	</label>

	<label>
		<h2>Content</h2>
		<textarea {...createPost.fields.content.as('text')}></textarea>
	</label>

	<button>Publish!</button>
</form>

Supported field types

Fields can be nested in objects and arrays, with values as:

Strings
Numbers
Booleans
File objects

Validation

If submitted data doesn’t pass the schema, each invalid field’s issues() method returns error objects:

<form {...createPost}>
	<label>
		<h2>Title</h2>

		{#each createPost.fields.title.issues() as issue}
			<p class="issue">{issue.message}</p>
		{/each}

		<input {...createPost.fields.title.as('text')} />
	</label>

	<!-- more fields -->

	<button>Publish!</button>
</form>

You can validate programmatically:

<form {...createPost} oninput={() => createPost.validate()}>
	<!-- fields -->
</form>

Single-flight mutations

Specify which queries should be refreshed in response to a form submission:

import { query, form } from '$app/server';

export const getPosts = query(async () => { /* ... */ });

export const createPost = form(
	v.object({/* ... */}),
	async (data) => {
		// form logic...

		// Refresh getPosts() on the server
		await getPosts().refresh();

		redirect(303, `/blog/${slug}`);
	}
);

enhance

Customize form submission behavior:

<!--- file: src/routes/blog/new/+page.svelte --->
<script>
	import { createPost } from '../data.remote';
	import { showToast } from '$lib/toast';
</script>

<form {...createPost.enhance(async ({ form, data, submit }) => {
	try {
		await submit();
		form.reset();
		showToast('Successfully published!');
	} catch (error) {
		showToast('Oh no! Something went wrong');
	}
})}>
	<!-- fields -->
</form>

command

The command function allows you to write data to the server from anywhere (unlike form, which is element-specific):

/// file: likes.remote.js
import * as v from 'valibot';
import { query, command } from '$app/server';
import * as db from '$lib/server/database';

export const getLikes = query(v.string(), async (id) => {
	const [row] = await db.sql`
		SELECT likes FROM item WHERE id = ${id}
	`;
	return row.likes;
});

export const addLike = command(v.string(), async (id) => {
	await db.sql`
		UPDATE item
		SET likes = likes + 1
		WHERE id = ${id}
	`;
});

Prefer form where possible, since it gracefully degrades if JavaScript is disabled or fails to load.

Updating queries

Tell SvelteKit which queries need to be refreshed:

Inside command
When calling

export const addLike = command(v.string(), async (id) => {
	await db.sql`UPDATE item SET likes = likes + 1 WHERE id = ${id}`;
	getLikes(id).refresh();
});

<button
	onclick={async () => {
		try {
			await addLike(item.id).updates(getLikes(item.id));
		} catch (error) {
			showToast('Something went wrong!');
		}
	}}
>

Use withOverride for optimistic updates:

try {
	await addLike(item.id).updates(
		getLikes(item.id).withOverride((n) => n + 1)
	);
} catch (error) {
	showToast('Something went wrong!');
}

prerender

The prerender function is similar to query, except it’s invoked at build time:

/// file: src/routes/blog/data.remote.js
import { prerender } from '$app/server';
import * as db from '$lib/server/database';

export const getPosts = prerender(async () => {
	const posts = await db.sql`
		SELECT title, slug
		FROM post
		ORDER BY published_at DESC
	`;

	return posts;
});

Use this for data that changes at most once per redeployment. You can use prerender functions on pages that are otherwise dynamic, allowing for partial prerendering.

Prerender arguments

Specify which values should be prerendered using the inputs option:

import * as v from 'valibot';
import { prerender } from '$app/server';

export const getPost = prerender(
	v.string(),
	async (slug) => { /* ... */ },
	{
		inputs: () => [
			'first-post',
			'second-post',
			'third-post'
		]
	}
);

By default, prerender functions are excluded from your server bundle. Set dynamic: true to change this:

export const getPost = prerender(
	v.string(),
	async (slug) => { /* ... */ },
	{
		dynamic: true,
		inputs: () => ['first-post', 'second-post', 'third-post']
	}
);

Using getRequestEvent

Inside remote functions, use getRequestEvent to get the current RequestEvent object:

/// file: user.remote.ts
import { getRequestEvent, query } from '$app/server';
import { findUser } from '$lib/server/database';

export const getProfile = query(async () => {
	const user = await getUser();

	return {
		name: user.name,
		avatar: user.avatar
	};
});

const getUser = query(async () => {
	const { cookies } = getRequestEvent();
	return await findUser(cookies.get('session_id'));
});

Some properties of RequestEvent are different inside remote functions. Never use route, params, or url to determine user authorization.

Getting Started

Core Concepts

Build and Deploy

Advanced

Enabling remote functions

Overview

query

form

command

prerender

query

Query arguments

Refreshing queries

query.batch

form

Fields

Validation

Single-flight mutations

enhance

command

Updating queries

prerender

Prerender arguments

Using getRequestEvent

Next steps

Routing

Load functions

Getting Started

Core Concepts

Build and Deploy

Advanced

​Enabling remote functions

​Overview

query

form

command

prerender

​query

​Query arguments

​Refreshing queries

​query.batch

​form

​Fields

​Validation

​Single-flight mutations

​enhance

​command

​Updating queries

​prerender

​Prerender arguments

​Using getRequestEvent

​Next steps

Routing

Load functions

Enabling remote functions

Overview

query

Query arguments

Refreshing queries

query.batch

form

Fields

Validation

Single-flight mutations

enhance

command

Updating queries

prerender

Prerender arguments

Using getRequestEvent

Next steps