5 Advanced TypeScript Tips Every Dev Should Know

1. Branded Types for IDs

Never confuse a userId with a postId again:

type Brand<T, B> = T & { __brand: B };

type UserId = Brand<string, "UserId">;
type PostId = Brand<string, "PostId">;

function getUser(id: UserId) { /* ... */ }

const userId = "abc" as UserId;
const postId = "xyz" as PostId;

getUser(userId); // OK
getUser(postId); // Type error!

2. Template Literal Types

Create types from strings:

type HttpMethod = "GET" | "POST" | "PUT" | "DELETE";
type ApiRoute = `/api/${string}`;
type Endpoint = `${HttpMethod} ${ApiRoute}`;

// "GET /api/users" ✓
// "PATCH /api/users" ✗

3. satisfies for the best of both worlds

Validate the type without losing inference:

const config = {
  port: 3000,
  host: "localhost",
  debug: true,
} satisfies Record<string, string | number | boolean>;

// config.port is still `number`, not `string | number | boolean`

4. Recursive Conditional Types

type DeepReadonly<T> = T extends object
  ? { readonly [K in keyof T]: DeepReadonly<T[K]> }
  : T;

5. infer to extract types

type ReturnTypeOf<T> = T extends (...args: never[]) => infer R ? R : never;
type PromiseValue<T> = T extends Promise<infer V> ? V : T;

Mastering these patterns separates a good TypeScript dev from a great one.