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.

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

ts
/** @param {AdapterSpecificOptions} options */
export default function (options) {
    /** @type {import('@sveltejs/kit').Adapter} */
    const adapter = {
        name: 'adapter-package-name',
        async adapt(builder) {
            // adapter implementation
        }
    };

    return adapter;
}

The types for Adapter and its parameters are available in types/index.d.ts.

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.ts
  • 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/install-fetch helper for platforms that can use node-fetch
• 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].