retype

Reified types for Typescript.

About

Retype gives you a way declare types in a way that the typesystem can read and can also be checked at runtime. The need came from declaring API routes which we wanted to be able to parse for developer experience wins, while still being able to validate at runtime.

Install

yarn add @screenplaydev/retype

Usage

import * as t from "@screenplaydev/retype";

const isBlogPost = t.shape({
  title: t.string,
  content: t.string,
  author: t.optional(
    t.shape({
      name: t.string,
      age: t.number,
    })
  ),
});

type TBlogPost = t.TypeOf<typeof isBlogPost>;

isBlogPost({
  title: "Hello world",
  content: "Lorem ipsum...",
}); // returns true

isBlogPost({
  foo: "bar",
}); // returns false

API Reference

JSON-ifiable Basics

• t.nulltype
• t.number
• t.string
• t.array(t.string)
• t.shape({memberName: t.string})

JavaScript-isms

• t.undefinedtype
• t.literal("FOO" as const)
• t.tuple([t.string, t.number])
• t.union(t.string, t.number)
• t.intersection(t.shape({name: t.string}), t.shape({age: t.number}))

Type relations

• t.unionMany([t.number, t.string])
• t.intersectMany([t.shape({name: t.string}), t.shape({age: t.number})])
• t.literals(["FOO", "BAR"] as const)

Convenience

• t.optional(t.string)
• t.nullable(t.string)

Extension

Adding other validators is very simple, just add a function which returns a type predicate:

export const string = (value: unknown): value is string => {
  return typeof value === "string";
};

Inspiration

Heavily inspired by io-ts and runtypes.

(More alternatives here: https://www.typescriptneedstypes.com/)

License

MIT Licensed (see LICENSE.txt)

Copyright 2021, Screenplay Studios Inc.