Setting status code for exception raised in load() function in SvelteKit - sveltekit

Question

I have a load() route function that may throw a "maintenance mode" error if the backend is under maintenance. This may happen in __layout, load() or elsewhere in the frontend:
function load() {
if(looksLikeDataIsUnderMaintennce) throw new UnderMaintenanceError();
}
Then I am catching this error in __error.svelte to display a more specific error message instead of "HTTP 500 We are on fire".
<script context="module">
/** #type {import('#sveltejs/kit').Load} */
export function load({error, status}) {
const maintenance = error.name === "UnderMaintenanceError";
return {
props: {
title: `${status}`,
message: error.message,
maintenance: maintenance,
}
};
}
</script>
<script>
export let maintenance;
</script>
<div class="container">
{#if maintenance}
<h1 class="text-center">{chainName} data under maintenance, we are back in X minutes</h1>
{:else}
<h1 class="text-center">HTTP {title} error</h1>
<pre>{message}</pre>
{/if}
</div>
By default, SvelteKit serves exceptions with HTTP status code 500 (internal error). For maintenance, I would like to change the HTTP status code from 500 to more specific HTTP 503 Service Unavailable as that's the preferred HTTP status code for maintenance and temporarily unavailability. I could not find a direct way to do this - returning status from __error.load does not seem to do the trick.
Is there a way to change the HTTP status code for thrown exceptions and error handler in SvelteKit?

Answer 1

You can return an object with a status property, like in this example from the docs. That will automatically show the error page. You can pass more props if you want more information about the error.
So something like this:
export async function get() {
// If under maintenance
return {
status: 503
};
}
UPDATE:
For some reason, I can't get the error message to propagate in the get endpoint function, so if you want to pass the error around it seems you need to use the load function from that page, like so:
<script lang='ts' context='module'>
export function load({ error }) {
console.log(error);
return {
status: 503,
error: new UnderMaintenanceError(),
}
}
</script>
I don't know if I'm missing something or if it's just a bug.

Answer 2

Based on Odilf's answer, we were able to this in the load() function in __layout:
<script context="module">
import { checkChainMaintenance } from "$lib/chain/maintenance";
/** #type {import('#sveltejs/kit').Load} */
export function load({ params }) {
// Check for the data maintenance status.
// If under maintenance, trigger __error with a special
// layout and message.
try {
checkChainMaintenance(params.chain);
} catch(error) {
return { status: 503, error };
}
return {};
}
</script>
<slot />
See full example.