Sample

Custom transformers and registered classes in SuperJSON require strict JSONValue outputs and bypass constructors on deserialization, breaking private fields, getter allowProps, subclass lookups and symbol keys

sha256:71dddfbeedcacf9af39b6800da5d8475a755310450b3a3c1a2bf78ec5a5deec9

Case

Goal

Custom transformers and registered classes in SuperJSON require strict JSONValue outputs and bypass constructors on deserialization, breaking private fields, getter allowProps, subclass lookups and symbol keys HOW

Packages

superjson 2.2.6

Environment

node

Created

2026-08-16T06:23:09Z

Contract

• assert registerCustom takes (transformer, name) in that order, and its serialize function must return a pure JSONValue because superjson does not recursively annotate custom transformer output
• assert returning a Date from a custom transformer's serialize produces an unannotated string in json that deserializes as a string rather than a Date
• assert returning a BigInt from a custom transformer's serialize leaves raw bigint in json and causes superjson.stringify to throw TypeError
• assert registerClass deserializes via Object.create(prototype) + Object.assign without calling the constructor, leaving JS private fields uninitialized and throwing TypeError on access
• assert passing a prototype getter into registerClass allowProps serializes the getter value but throws TypeError on deserialization when Object.assign tries to assign to a getter-only property
• assert registering a parent class does not cover subclass instances because constructor matching is exact, silently degrading subclass instances to plain objects after parse
• assert registering a symbol allows symbol values to round-trip, but symbol-keyed object properties are silently omitted because superjson iterates enumerable keys via Object.entries
• assert serialize throws an explicit prototype pollution Error if an object contains an own property named constructor, __proto__, or prototype
• assert meta.referentialEqualities is an array tuple when root is referenced in a cycle but an object record when referencing nested siblings
• assert new SuperJSON({ dedupe: true }) replaces duplicate references with null in json while default instance preserves full subtree in json
• assert deserialize with inPlace: true mutates the input payload json while default deserialize copies it

Files

• NOTES.md
• csx.json
• package-lock.json
• package.json
• src/custom-and-classes.mjs
• test/contract.mjs

Download the verified artifact (tar.gz) — the exact bytes the contract ran against

Origin Seeder

csx-seed

Verification receipts

• node 22 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · node-typescript@1 · 2026-08-16 · ed25519:d91480838ac982c9