5 TypeScript Patterns Every Developer Should Know in 2026

TypeScript has evolved massively. Here are 5 patterns I use daily that make my code bulletproof.

1. Discriminated Unions for State Management

type State = 
  | { status: "idle" }
  | { status: "loading" }
  | { status: "success"; data: User[] }
  | { status: "error"; error: string };

function handleState(state: State) {
  switch (state.status) {
    case "success":
      return state.data; // TS knows data exists here
    case "error":
      return state.error; // TS knows error exists here
  }
}

The compiler narrows the type automatically. No more if (data !== undefined) everywhere.

2. satisfies for Type-Safe Configs

const config = {
  apiUrl: "https://api.example.com",
  timeout: 5000,
  retries: 3,
} satisfies Record<string, string | number>;

// config.apiUrl is still typed as string, not string | number
config.apiUrl.toUpperCase(); // ✅ Works!

satisfies validates the type without widening it.

3. Template Literal Types for API Routes

type ApiRoute = `/api/${string}`;
type UserRoute = `/api/users/${number}`;

function fetchApi(route: ApiRoute) { /* ... */ }

fetchApi("/api/users/123"); // ✅
fetchApi("/dashboard");      // ❌ Type error

4. Const Assertions for Readonly Everything

const ROLES = ["admin", "user", "viewer"] as const;
type Role = (typeof ROLES)[number]; // "admin" | "user" | "viewer"

// Instead of: type Role = string

5. Branded Types for Domain Safety

type UserId = string & { __brand: "UserId" };
type PostId = string & { __brand: "PostId" };

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

const userId = "abc" as UserId;
getUser(userId); // ✅
getPost(userId); // ❌ Type error — can't mix IDs

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Which TypeScript patterns do you use the most? Drop your favorites below!

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