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Beyond basic types — discriminated unions, branded types, template literals, and the patterns that make large TypeScript codebases maintainable under pressure.
TypeScript has won. But most teams use 10% of what it offers, missing the patterns that make it genuinely powerful at scale.
Discriminated unions for state
The most impactful pattern: model every piece of state as a discriminated union. Instead of loading: boolean, error: string | null, data: T | null, use a union that makes impossible states impossible.
type AsyncState<T> =
| { status: "idle" }
| { status: "loading" }
| { status: "success"; data: T }
| { status: "error"; message: string };Branded types for domain primitives
A UserId and an OrderId are both strings, but they should never be confused. Branded types let you enforce this at compile time with zero runtime cost.
Template literal types for type-safe routing
If you have a routing system, you can express valid route patterns as template literal types, catching typos and missing params at compile time rather than at runtime in production.
const satisfies for config objects
The satisfies operator (TS 4.9+) lets you validate that an object matches a type while preserving the most specific literal types. Perfect for config objects, navigation definitions, and theme tokens.
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