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