ts-simple-type VS spartan-schema

We use an internal validator library that we infer request types from. It’s similar to Zod (but also predates it by a year).

I’ve also spent some time on a Typescript type to X compiler. My first prototype is open source and targets Thrift, Proto3, Python, and JSON schema: https://github.com/justjake/ts-simple-type/tree/main/src/com...

I’m not happy with the design decision in that codebase to try to “simplify” Typescript types before compiling, and probably won’t continue that implementation, but we have a few internal code generators that consume TS types and output test data builders and model clases we use in production.

After some frustration with the TypeScript schema library ecosystem, I've decided that I'd prefer to declare my types using TypeScript's excellent type syntax, so I can take advantage of generics, mapped types, etc. Then, I'll take those TypeScript types and compile them to whatever alternative schema format I need.

There are many libraries that claim to convert your Typescript types to other formats, such as ts-json-schema-generator, ts-to-zod, or typeconv/core-types-ts. These libraries work by interpreting the Typescript AST, essentially re-implementing a bare-bones type system from scratch. Most do not support advanced Typescript features like generic application, mapped types, or string literal types. So, what's the point? To avoid those limitations, I use Typescript's first-party ts.TypeChecker API to analyze types, and an existing library called ts-simple-type (which I've forked) to convert from ts.Type to a more usable intermediate format. Then, I recurse over the intermediate format and emit "AST nodes". It's pretty simple, but seems promising.

So far, I have compilers from TypeScript type to Python 3 and Thrift. But I plan to add OpenAPI/JSONSchema, Protobuf (Proto3), Kotlin, Swift, and maybe Zod and Avro. Each target language is around ~300 LoC so they're pretty easy to put together.

Repo: https://github.com/justjake/ts-simple-type

Compiler input and output: https://github.com/justjake/ts-simple-type/blob/jake--compil...

Thrift compiler: https://github.com/justjake/ts-simple-type/blob/jake--compil...

Python compiler: https://github.com/justjake/ts-simple-type/blob/jake--compil...

In the same vein, shameless plug for my own library, Spartan Schema:

https://github.com/ar-nelson/spartan-schema

It does the same thing as Zod, but is much smaller/simpler and its types always have a JSON representation.