// Create nominal types to prevent primitive obsession
type Brand<K, T> = K & { __brand: T };
type UserId = Brand<string, 'UserId'>;
type OrderId = Brand<string, 'OrderId'>;

// Prevents accidental mixing of domain primitives
function processOrder(orderId: OrderId, userId: UserId) { }

// Recursive type manipulation
type DeepReadonly<T> = T extends (...args: any[]) => any 
  ? T 
  : T extends object 
    ? { readonly [K in keyof T]: DeepReadonly<T[K]> }
    : T;

// Template literal type magic
type PropEventSource<Type> = {
  on<Key extends string & keyof Type>
    (eventName: `${Key}Changed`, callback: (newValue: Type[Key]) => void): void;
};

// Use 'satisfies' for constraint validation (TS 5.0+)
const config = {
  api: "https://api.example.com",
  timeout: 5000
} satisfies Record<string, string | number>;
// Preserves literal types while ensuring constraints

// Const assertions for maximum inference
const routes = ['/home', '/about', '/contact'] as const;
type Route = typeof routes[number]; // '/home' | '/about' | '/contact'

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**Build Performance Patterns**
- Enable `skipLibCheck: true` for library type checking only (often significantly improves performance on large projects, but avoid masking app typing issues)
- Use `incremental: true` with `.tsbuildinfo` cache
- Configure `include`/`exclude` precisely
- For monorepos: Use project references with `composite: true`

// types/ambient.d.ts
declare module 'some-untyped-package' {
  const value: unknown;
  export default value;
  export = value; // if CJS interop is needed
}

// Bad: Infinite recursion
type InfiniteArray<T> = T | InfiniteArray<T>[];

// Good: Limited recursion
type NestedArray<T, D extends number = 5> = 
  D extends 0 ? T : T | NestedArray<T, [-1, 0, 1, 2, 3, 4][D]>[];

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**Tool Migration Decisions**

| From | To | When | Migration Effort |
|------|-----|------|-----------------|
| ESLint + Prettier | Biome | Need much faster speed, okay with fewer rules | Low (1 day) |
| TSC for linting | Type-check only | Have 100+ files, need faster feedback | Medium (2-3 days) |
| Lerna | Nx/Turborepo | Need caching, parallel builds | High (1 week) |
| CJS | ESM | Node 18+, modern tooling | High (varies) |

// Root tsconfig.json
{
  "references": [
    { "path": "./packages/core" },
    { "path": "./packages/ui" },
    { "path": "./apps/web" }
  ],
  "compilerOptions": {
    "composite": true,
    "declaration": true,
    "declarationMap": true
  }
}

// in avatar.test-d.ts
import { expectTypeOf } from 'vitest'
import type { Avatar } from './avatar'

test('Avatar props are correctly typed', () => {
  expectTypeOf<Avatar>().toHaveProperty('size')
  expectTypeOf<Avatar['size']>().toEqualTypeOf<'sm' | 'md' | 'lg'>()
})

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// Proper error class with stack preservation
class DomainError extends Error {
  constructor(
    message: string,
    public code: string,
    public statusCode: number
  ) {
    super(message);
    this.name = 'DomainError';
    Error.captureStackTrace(this, this.constructor);
  }
}

{
  "compilerOptions": {
    "strict": true,
    "noUncheckedIndexedAccess": true,
    "noImplicitOverride": true,
    "exactOptionalPropertyTypes": true,
    "noPropertyAccessFromIndexSignature": true
  }
}

Type checking only? → tsc
Type checking + linting speed critical? → Biome  
Type checking + comprehensive linting? → ESLint + typescript-eslint
Type testing? → Vitest expectTypeOf
Build tool? → Project size <10 packages? Turborepo. Else? Nx

Slow type checking? → skipLibCheck, incremental, project references
Slow builds? → Check bundler config, enable caching
Slow tests? → Vitest with threads, avoid type checking in tests
Slow language server? → Exclude node_modules, limit files in tsconfig