Hi @michaeljonsampson! Thanks for opening this PR. When you opened the issue, I somehow thought that Decimal was a built-in type like BigInt. It's apparently a proposal in Stage 1: https://github.com/tc39/proposal-decimal

To keep bundle size down, SuperJSON needs to stay as lean as possible. I've adapted your changes into #159, which adds a test for Decimal.js and mentions how to integrate in the README.

@Skn0tt wasn't my issue but I ran into the same problem an came across it. Didn't know about registerCustom. That covers my use case. Tested #159 and I can still serialize Prisma.Decimal. Thanks.

Just a heads up for anyone using superjson with tRPC Data Transformers, make sure to put the Decimal.js registerCustom recipe in both your client and router.

I'd recommend making a utils/superjson.ts file and importing superjson from there, to keep them in sync.

Hi @michaelhays ... do you have a minimal reproduction of your superjson transformer with decimal.js support? I'd love to use it one of our projects ...

Sure, here are the relevant files for a Next.js project:

import Decimal from 'decimal.js'
import superjson from 'superjson'

superjson.registerCustom<Decimal, string>(
  {
    isApplicable: (v): v is Decimal => Decimal.isDecimal(v),
    serialize: (v) => v.toJSON(),
    deserialize: (v) => new Decimal(v),
  },
  'decimal.js',
)

export default superjson

import type { AppRouter } from '@/server/appRouter'
import { createTRPCNext } from '@trpc/next'
import superjson from './superjson'

export const trpc = createTRPCNext<AppRouter>({
  config() {
    return {
      transformer: superjson,
      links: [...],
    }
  },
})

import { initTRPC, TRPCError } from '@trpc/server'
import superjson from '../utils/superjson'
import type { Context } from './context'

const t = initTRPC.context<Context>().create({ transformer: superjson })

export const publicProcedure = t.procedure

Thank you for the code examples. The workaround for Decimal.js works with trpc, but how do I register custom when using it with the next-superjson-plugin (swc)? I'm unable to pass Decimal properties as props from a Server Component to a Client Component.

You need to execute the registerCustom call is on both the client and the server. I‘m unsure what the right files for that are in Next.js nowadays - maybe something like app.server.js and app.client.js, if they exist? Let us know what works for you, i‘m sure this is super useful for many folks.

Yes, I did try this. I added the registerCustom function on the server component level (at layout.tsx) and inside a client component (inside a useEffect of a ClientComponent and outside). Adding it to the client component seemed to do nothing, but adding it on the server component threw the same error.

I'm not sure if there's a way to run a function before the build even begins, with either webpack or SWC, that might be a good place to add this.

Did you find a solution?

@AmruthPillai

@pedro757 Nope, just reverted back to using Number datatype in Prisma for now. Would love to make use of Decimal, but I believe this is something Next.js needs to get straight, adding middlewares for client and server individually, and not just a single Edge runtime variant.

I was able to make it work, setting the registerCustom in a page.tsx and in passing data-superjson prop to client component

// page.tsx
import { Temporal } from "temporal-polyfill";
import Button from "./client";
import SuperJSON from "superjson";
import PlainDate, { startOfMonth, weekNumber } from 'plain-date'
SuperJSON.registerCustom<Temporal.PlainDate, string>(
{
  isApplicable: (v): v is Temporal.PlainDate =>
    v instanceof Temporal.PlainDate ||
    (typeof v === "string" &&
      RegExp(
        /^(19[0-9]{2}|2[0-9]{3})-(0[1-9]|1[012])-([123]0|[012][1-9]|31)$/,
      ).test(v)),
  serialize: (v) => v.toJSON(),
  deserialize: (v) => Temporal.PlainDate.from(v),
},
"PlainDate",
)

export default function Home() {
return (
  <main className="flex min-h-screen flex-col items-center justify-between p-24">
    <Button date={new Temporal.PlainDate(2023, 1, 1)} data-superjson />
  </main>
);
}

With that I receive my custom type in the client component

@AmruthPillai