Cannot stringify arbitrary non-POJOs

[wvhulle]

When adding a +page.server.ts file and filling it with the contents

import { json } from "@sveltejs/kit";

export async function load({ params }) {
    return json()
}

SvelteKit throws the error

DevalueError: Cannot stringify arbitrary non-POJOs
    at walk (file:///home/<project>/node_modules/.pnpm/[email protected]/node_modules/devalue/src/uneval.js:83:13)

Is this a regression in SvelteKit caused by devalue bumping to 4.0.0?

[geoffrich]

This is expected. You only return POJOs (plain-old-javascript-objects) from load functions, e.g.

export async function load({ params }) {
    return { hello: 'world', count: 2 }
}

The json helper creates a Response, which you can't return from load. Only +server.js files return Responses.

[wvhulle]

Thank you, yes I figured it out. Maybe the error could be clearer.

[Rich-Harris]

Opened an issue #7262

[RossAddinall]

Just a quick note on this. I'm new to Svelte coming from React.
It seems odd to me that you can use the "fail" helper in a +page.server.js but not the "json" helper.
See this example.

[geoffrich]

What are you trying to do that requires returning json(...) in a +page.server.js? json is only intended for use in +server.js endpoints that require you to return a Response object. There is no need for it in +page.server.js

In +page.server.js you just return data objects directly, e.g.

// ✅ do this!
export function load() {
    return { hello: 'world' };
}

// ❌ don't do this!
export function load() {
    return json({ hello: 'world' });
}

[RossAddinall]

@geoffrich Yes, I realise that now. I was trying to be smart and saw that the example used "fail" and in my enthusiasm thought I would use "json" to return the successful result. Now that I understand that "json" forms a Response object I can see that is not what I want to do, but initially I saw "fail", "json" etc. as a set of helpers and naively if I could use one I could use them all.

Thanks for your clarification, hopefully, this might help someone else.

[ridly]

Hello guys,

I know I'm late for the party. I just ran into this problem myself when using Prisma.Decimal field type in the database. I found that superjson can serialize / deserialize it, including other complex types like Date, BigInt.
I'm wondering if we can replace sveltekit's JSON.stringify / JSON.parse with superjson? (https://github.com/flightcontrolhq/superjson)
Let me know.

Cheers
Tamas

[Rich-Harris]

#7259 (comment)

[Rich-Harris]

You can now use the transport hook to define custom encoders and decoders.

[ridly]

Thanks @Rich-Harris , I'll give it a go. You have a solution for everything.