Question 1

How to use ts-pattern for state management in React?

Accepted Answer

TS-Pattern integrates seamlessly with React useReducer for exhaustive action handling. The README provides a state reducer example where patterns match both state and event types, ensuring all transitions are type-safe and maintainable, reducing bug-prone conditional logic.

Question 2

ts-pattern vs switch statements: which is better for TypeScript?

Accepted Answer

TS-Pattern offers exhaustive checking and superior type inference over switch statements, which can miss cases and require manual type guards. Use ts-pattern for complex, type-safe conditions; switch may suffice for simple, non-exhaustive scenarios, but ts-pattern's expressiveness shines with nested data.

Question 3

How to extract multiple values with P.select in ts-pattern?

Accepted Answer

Use named selections like P.select('name') to extract multiple values into a selections object passed to the handler. For example, in an object pattern, select properties like user and content, then access them in the handler as shown in the P.select patterns documentation.

Question 4

Does ts-pattern work with JavaScript or only TypeScript?

Accepted Answer

TS-Pattern is designed for TypeScript and relies on its type system for features like exhaustiveness and inference. It can run in JavaScript but without type safety, limiting its core benefits; patterns still match at runtime, but compile-time checks are lost.

Question 5

Why is my ts-pattern exhaustive check failing?

Accepted Answer

Exhaustive checks fail when not all union type cases are handled. Ensure every possible input variant has a corresponding .with() clause or use .otherwise() for a default. Review your types to confirm coverage, as illustrated in the exhaustive checking examples with error handling.

Question 6

How to add custom conditions with ts-pattern guards?

Accepted Answer

Use P.when() within patterns or pass a guard function as the second argument to .with() for custom logic. For instance, P.when((x) => x > 10) matches numbers greater than 10, enabling non-trivial conditions, detailed in the guard functions section with examples.

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