TypeScript Union Type Generator

Generates TypeScript union types straight from raw payloads (live demo).

Transforms this:

{
  First: { type: "first", value: "two" },
  Second: { type: "second", val: 1 },
};

into:

type First = { type: "first"; value: string };
type Second = { type: "second"; val: number };
type Union = First | Second;

Installation

npm install tsug

Usage

To generate a Union Type from a bunch of payloads, you can run

import { generateUnion } from "ts-union-generator";

const events = {
  UserCreate: {
    type: "user-create",
    id: 12,
    username: "atomrc",
  },
  UserDelete: {
    type: "user-delete",
    id: 12,
  },
};
const types = generateUnion(payloads);
// ^ your union type and type definitions are in that string

Discriminant detection

By default the library will take the first property that is common to every single payload that you give.
If no common property can be found, it will just generate the raw types.

If needed you can provide the property that should be the discriminant as second parameter:

const payloads = {
  First: { value: "val", type: "first" },
  Second: { value: "tough", type: "second" },
};

const types = generateUnion(payloads, { discriminant: "type" });
/*
type First = { value: string, type: "first" };
type Second = { value: string, type: "second" };
type Union = First | Second;
*/

Merge multiple payload for the same type

It is possible to provide multiple paylaods for a single type you want to generate. In this case, the payloads will be merged together and optional properties will be infered from them.

const payloads = {
  First: [
    // notice the array for the type First
    { type: "first", name: "felix", age: 10 },
    { type: "first", name: "sam" },
  ],
  Second: { type: "second", value: "tough" },
};

const types = generateUnion(payloads);
/*
type First = { type: "first", name: string, age?: number };
type Second = { type: "second", value: string };
type Union = First | Second;
*/

Extract common properties to a Base type

You might want to extact properties that are common between all the types. In this case you can pass { extractCommon: true } option to the generateUnion function

const payloads = {
  First: { type: "a", value: "first" },
  Second: { type: "b", value: "second" },
  Third: { type: "c", value: "third" },
};

const types = generateUnion(payload, { extractCommon: true });
/*
type Base = { value: string };
type First = Base & { type: "a" };
type Second = Base & { type: "b" };
type Third = Base & { type: "c" };
type Union = First | Second | Third;
*/