SvelteKitBuild and deploy

Writing adapters

If an adapter for your preferred environment doesn’t yet exist, you can build your own. We recommend looking at the source for an adapter to a platform similar to yours and copying it as a starting point.

Adapter packages implement the following API, which creates an Adapter:

/** @param {AdapterSpecificOptions} options */
export default function (options: any@paramoptions options) {
	/** @type {import('@sveltejs/kit').Adapter} */
	const const adapter: Adapter@type{import('@sveltejs/kit').Adapter}adapter = {
		Adapter.name: stringThe name of the adapter, using for logging. Will typically correspond to the package name.
name: 'adapter-package-name',
		async Adapter.adapt(builder: Builder): MaybePromise<void>This function is called after SvelteKit has built your app.
@parambuilder An object provided by SvelteKit that contains methods for adapting the appadapt(builder: Builderbuilder) {
			// adapter implementation
		},
		async Adapter.emulate?(): MaybePromise<Emulator>Creates an Emulator, which allows the adapter to influence the environment
during dev, build and prerendering
emulate() {
			return {
				async Emulator.platform?(details: {
    config: any;
    prerender: PrerenderOption;
}): MaybePromise<App.Platform>A function that is called with the current route config and prerender option
and returns an App.Platform object
platform({ config: anyconfig, prerender: PrerenderOptionprerender }) {
					// the returned object becomes `event.platform` during dev, build and
					// preview. Its shape is that of `App.Platform`
				}
			}
		},
		Adapter.supports?: {
    read?: (details: {
        config: any;
        route: {
            id: string;
        };
    }) => boolean;
} | undefinedChecks called during dev and build to determine whether specific features will work in production with this adapter
supports: {
			read?: ((details: {
    config: any;
    route: {
        id: string;
    };
}) => boolean) | undefinedTest support for read from $app/server
@paramconfig The merged route configread: ({ config: anyconfig, route: {
    id: string;
}route }) => {
				// Return `true` if the route with the given `config` can use `read`
				// from `$app/server` in production, return `false` if it can't.
				// Or throw a descriptive error describing how to configure the deployment
			}
		}
	};

	return const adapter: Adapter@type{import('@sveltejs/kit').Adapter}adapter;
}

Of these, name and adapt are required. emulate and supports are optional.

Within the adapt method, there are a number of things that an adapter should do:

Clear out the build directory
Write SvelteKit output with builder.writeClient, builder.writeServer, and builder.writePrerendered
Output code that:
- Imports Server from ${builder.getServerDirectory()}/index.js
- Instantiates the app with a manifest generated with builder.generateManifest({ relativePath })
- Listens for requests from the platform, converts them to a standard Request if necessary, calls the server.respond(request, { getClientAddress }) function to generate a Response and responds with it
- expose any platform-specific information to SvelteKit via the platform option passed to server.respond
- Globally shims fetch to work on the target platform, if necessary. SvelteKit provides a @sveltejs/kit/node/polyfills helper for platforms that can use undici
Bundle the output to avoid needing to install dependencies on the target platform, if necessary
Put the user’s static files and the generated JS/CSS in the correct location for the target platform

Where possible, we recommend putting the adapter output under the build/ directory with any intermediate output placed under .svelte-kit/[adapter-name].

Edit this page on GitHub

previous next

Vercel Advanced routing