ts-simple-type VS openapi-typescript-codegen

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...

I’d also add that if you use Typescript with an OpenAPI client generator (https://github.com/ferdikoomen/openapi-typescript-codegen) it can immensely alleviate some of the biggest pain points of seperate backend and front-end. It always used to be a major pain in the ass with the amount of overhead an API change would incur - updating documentation, postman, constant communication between backend and front-end devs, etc. Now I just npm run generate, I see new API changes in my Git client and Typescript errors for code that needs updating.

Also, using a library like Tanstack Query or Rdtk Query can almost completely eliminate manual state management, and kinda makes the whole development experience feel almost like SSR.

I have been in love with Loopback.io since v2 even though it was a bit of a rollercoaster.. Loopback v4 is a beautiful library. Its been around longer than nestjs but that's the easiest thing to compare it too. I recently have been creating lb4 servers that interface nextjs and react native clients. Initially, I identify my entities and use cases that I want to build. I then use the lb4 cli to auto generate models, relations, controllers, datasources, interceptors (add logic on methods/classes). I can start testing them with the OpenAPI explorer. With the openapi-typescript-codegen library I can generate services from my lb4 OpenAPI spec that I can use on the client side. From there, you can really query data easily with the loopback filter (which can be used on the client too). I initially started doing this with angular1/2+ but its been pleasant using many clients. Even though I have been leveraging it for years in production, I am still learning and exploring. There are many other awesome things I can expand on or explain if you are interested!

https://loopback.io/doc/en/lb4/

https://github.com/ferdikoomen/openapi-typescript-codegen/tr...

In our current project with a TS frontend and Python backend, we use an OpenAPI schema as the source of truth and openapi-typescript-codegen [0] to interface with it on the client side. While not perfect, it provides a very nice interface to our API with request/response typings.

I also wrote a 10-line mock API wrapper that you can call as mockApi((request) => response), and it will type-check that your mock function implements the API correctly.

[0]: https://github.com/ferdikoomen/openapi-typescript-codegen

Second step is to generate typescript types from the backend's spec. You can use a library like this.

openapi-typescript-codegen Generates a Typescript client with interfaces from an OpenAPI spec.

I'm not familiar with all the options openapi-generator has. I tried it awhile ago and found it quite buggy, and more of a pain to run, especially if you're not already doing Java development. I ended up preferring OpenAPI Typescript Codegen, which is written in Typescript. One option it has which would solve the problem you're running into here, is that you can tell it to use union types instead of enums. So your interfaces would be generated as

I'm currently working on two separate projects, the first is a Django project with DRF and I codegen with drf-spectacular [1] and openapi-typescript-codegen [2]. The other project also uses Django, with the API through Hasura and codegen with graphql-codegen [3]. In both of these cases I've been able to largely avoid duplicating my models clientside, or at least it isn't manual.

1: https://github.com/ferdikoomen/openapi-typescript-codegen

2: https://drf-spectacular.readthedocs.io/en/latest/

3: https://github.com/dotansimha/graphql-code-generator

For typescript client code generation, I typically use something like openapi-typescript-codegen, but there are a lot more generators (like the openapi-generator project) that are imperfect in their own ways, I'm sure you can find one that works for you.