prettify-ts

Prettify<T> utility type that flattens TypeScript intersection types into readable single-object types, while preserving built-in types (Map, Set, Date, Promise, DOM types, TypedArrays, etc.).

Includes a TypeScript Language Service Plugin that shows the prettified type in VS Code hover tooltips.

Installation

npm install -D prettify-ts
# or
yarn add -D prettify-ts
# or
pnpm add -D prettify-ts

Scripts

| Command | Description | | ------------------------ | ------------------------------------------- | | npm run dev | Start dev server | | npm run build | Production build (types + plugin + library) | | npm run test | Run tests (watch mode) | | npm run test:run | Run tests once | | npm run test:typecheck | Run type-level tests | | npm run format | Format code | | npm run lint | Lint code | | npm run setup | Configure git hooks |

Usage — the type

import type { Prettify } from "prettify-ts";

interface A {
  x: string;
}
interface B {
  y: number;
}

type FlatVanilla = A & B; // ❌ Hover shows: A & B
type Flat = Prettify<A & B>; // ✅ Hover shows: { x: string; y: number }

Built-in types are preserved (not expanded into their internal members):

type Example = Prettify<{ id: string } & { data: Map<string, number> }>;
// → { id: string; data: Map<string, number> }

Usage — VS Code plugin

Add to your project's tsconfig.json:

{
  "compilerOptions": {
    "plugins": [{ "name": "prettify-ts" }]
  }
}

Then in VS Code, make sure you're using the workspace TypeScript version (Cmd+Shift+P → "TypeScript: Select TypeScript Version" → "Use Workspace Version").

Hovering over any type will show the default tooltip plus a Prettified section below it with the fully resolved type.