Provide reducers/reviviers for devalue in superForm/superValidate functions

[ktarmyshov]

Is your feature request related to a problem? Please describe.
I'm using Decimal.js in zod schemas. When I use the superForm with dataType='json', posting data fails during devalue.stringify, because it cannot serialize custom type "Decimal".

Describe the solution you'd like
Feature request: provide possibility to pass reducers/revivers to superForm/superValidate to parse the request data accordingly.

Describe alternatives you've considered

    async onSubmit(input) {
      // Reduce custom types before submitting
      const formData = await superFormResult.validateForm();
      if (formData.valid) {
        const formJsonData = JSON.parse(JSON.stringify(formData.data));
        input.jsonData(formJsonData);
      }
    },

I also tried to fork and npm-link the devalue package for sveltekit (to provide default reducers/revivers for sveltekit), but superforms is using 4.3.3 and sveltekit 5.0.0 (which may still be different in the future). Even if I "override" the dependency to use 5.0.0, this one instantiated in a different (memory) context and default reducers/revivers working for sveltekit are empty for superforms - so "no go".

Additional context
None

[AndreasHald]

This would be really interesting and it's something we wan't aswell. We use the MongoDB ObjectId class.

There is a discussion about this in svelte kit aswell sveltejs/kit#9401 maybe if implemented there it would solve these issues aswell?

[AndreasHald]

I tried creating a PR for this, by creating an object like this

export class Vector {
    x: number;
    y: number;
	constructor(x: number, y: number) {
		this.x = x;
		this.y = y;
	}
	magnitude() {
		return Math.sqrt(this.x * this.x + this.y * this.y);
	}
}


export const complexTypes: CustomTypeOptions = {
    reducers: {
        Vector: (value) => value instanceof Vector && [value.x, value.y]
    },
    revivers: {
        Vector: ([x,y]) => new Vector(x,y)
    },
    defaults: {
        Vector: () => new Vector(0,0)
    }
}

and providing it to SuperForms, a lot of stuff ends up working. But it breaks when you return data from a load function to the form, in the end at least as far as I can see, this needs to happen at a svelte kit level.

[ciscoheat]

It seems like sveltejs/kit#9401 doesn't make any progress, so maybe this can be an addition for v3. Need to think about a good interface for it though, as the basic return { form } won't work directly.

[shyakadavis]

@ciscoheat This was merged: sveltejs/kit#13149 Maybe it could help? 🤷

[ciscoheat]

It looks promising, I've just tested if transport could be imported from hooks to the client, and it worked, so if that object is passed to superValidate and superForm as an option, it should be possible.

[ciscoheat]

Have it working now, will be included in the next release!

[ktarmyshov]

Checking with my app, one form action returning custom type - worked out, need to check, if I have to DTO them before posting or it will work as well

[ktarmyshov]

seems to be working, all my dto funcs can be cleaned up.
thank you!