SvelteKitAdvanced

Errors

Errors are an inevitable fact of software development. SvelteKit handles errors differently depending on where they occur, what kind of errors they are, and the nature of the incoming request.

Error objects

Every error passes through the handleError hook — which can log it and customise it — before it is rendered. The hook’s kind property identifies where the error came from: your app ('app'), SvelteKit ('framework'), validation of a remote function argument ('validation') or an unknown source ('unknown'). By default, all are represented as simple { status: number, message: string } objects.

You can add additional properties, like a code or a tracking id, as shown in the examples below. (When using TypeScript this requires you to redefine the Error type as described in Type safety below).

App errors

An app error is one thrown from your app code using the error function imported from @sveltejs/kit:

src/routes/blog/[slug]/+page.server

import { error(alias) function error(status: {
    status: number;
    message: string;
} extends App.Error ? number : never, message?: string | undefined): never (+2 overloads)
import errorThrows an error with a HTTP status code and an optional message.
When called during request handling, this will cause SvelteKit to
return an error response; the error will be passed to handleError as an expected error.
Make sure you're not catching the thrown error, which would prevent SvelteKit from handling it.