README.md

Typescript type makeup

AKA Compile-time type-based transformers

⚠️ Moved to separate repos in Typescript Type Makeup org ⚠️

The idea of the project is that since we don't have an access to typescript types in the runtime (they're a subject to a type erasure), we can still emit some code to the runtime on compilation step. So this repository purpose is to

1. Brigde the gap between the idea and implementation by providing several helpers, such as ts-type-visitor, more on that later
2. Provide some ready-made libraries, such as superstruct-ts-transformer which a json validation library

Why makeup?

Because what makeup is that you wake up in the morning (compile time), go to the mirror (reflection) and do beautiful things (transformers) with your face (code). In the same manner we're using compile-time reflection on types via compiler api and do beautiful things out of them!

Superstruct transformer

Superstruct transformer Docs

It's a typescript transformer that will transforms validate<MyType>(JSON.parse("{}")) calls to an actual superstruct json validator

You write that code

import { validate } from "superstruct-ts-transformer";

type User = {
  name: string;
  alive: boolean;
};

const obj = validate<User>(JSON.parse('{ "name": "Me", "alive": true }'));

and it will become

import superstruct from "superstruct";
var obj = validate_User(JSON.parse('{ "name": "Me", "alive": true }'));

function validate_User(jsonObj) {
  var validator = superstruct.struct({
    name: "string",
    alive: "boolean"
  });
  return validator(jsonObj);
}

Looks cool, right? However it comes with a lot of limitations, take a look at the docs

Type visitor

Type visitor Docs

It's a visitor function for a type that gives you an easy-to-use (unlike typescript api) type tree. You can traverse it to either analyze it somehow or to emit someting to the runtime (e.g. json validation, react prop-types etc.). See docs for more info.