sveltejs/kit · warning

Passing an `App.Error` body as the second argument is deprec

Error message

Passing an `App.Error` body as the second argument is deprecated — pass the `message` as the second argument, and any additional properties as the third

What it means

`error(status, body)` in $app/utils warns in dev when the second argument is an object rather than a string. The object's `message` property is used and the rest become `properties`, but this overload is deprecated in favor of `error(status, message, properties)`.

Source

Thrown at packages/kit/src/exports/index.js:88

 * Throws 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.
 * @param {any} status The [HTTP status code](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status#client_error_responses). Must be in the range 400-599.
 * @param {any} [message] A string, or (deprecated) a partial App.Error object
 * @param {any} [properties] Additional properties of the App.Error type when passing a string message.
 * @return {never}
 * @throws {import('./public.js').HttpError} This error instructs SvelteKit to initiate HTTP error handling.
 * @throws {Error} If the provided status is invalid (not between 400 and 599).
 */
export function error(status, message, properties) {
	if ((!BROWSER || DEV) && (isNaN(status) || status < 400 || status > 599)) {
		throw new Error(`HTTP error status codes must be between 400 and 599 — ${status} is invalid`);
	}

	if (message !== undefined && typeof message !== 'string') {
		if (DEV) {
			console.warn(
				'Passing an `App.Error` body as the second argument is deprecated — pass the `message` as the second argument, and any additional properties as the third'
			);
		}

		({ message, ...properties } = message);
	}

	throw new HttpError({ ...properties, status, message: message ?? `Error: ${status}` });
}

/**
 * Checks whether this is an error thrown by {@link error}.
 * @template {number} T
 * @param {unknown} e
 * @param {T} [status] The status to filter for.
 * @return {e is (import('./public.js').HttpError & { status: T extends undefined ? never : T })}
 */
export function isHttpError(e, status) {

View on GitHub (pinned to 03f1687fe6)

Solutions

1. Split the call: pass the message string second and the remaining properties as a third argument
2. Search the codebase for `error(` calls whose second argument is an object literal
3. Update tests that assert on the deprecated overload

Example fix

// before
error(404, { message: 'Not found', code: 'MISSING' });
// after
error(404, 'Not found', { code: 'MISSING' });

// helper to migrate calls safely
function kitError(status, message, properties) {
  if (typeof message !== 'string') {
    const { message: msg, ...props } = message;
    return kitError(status, msg, props);
  }
  return { status, message, properties };
}

const isAppErrorBody = (m) => typeof m === 'object' && m !== null && typeof m.message === 'string';

// load/+server.js
import { error } from '@sveltejs/kit';
try {
  if (!user) throw error(404, 'Not found', { code: 'MISSING' });
} catch (e) {
  if (isHttpError(e)) return json({ code: e.body.code }, { status: e.status });
  throw e;
}

When it happens

Trigger: Calling `throw error(404, { message: 'Not found', code: 'X' })` in a load function or `+server.js` during dev (DEV only).

Common situations: Code written against older SvelteKit APIs before the three-argument signature existed; copied legacy error helpers.

Related errors

• `defineEnvVars` has moved — import it from `@sveltejs/kit/en
• HTTP error status codes must be between 400 and 599 — ${stat
• Error: ${status}
• Cannot `return error(...)` — use `error(...)` or `return fai
• The next HMR update will cause the page to reload

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/2d49fbb49a8a8373. Report an issue: GitHub.