typescript-best-practices

TypeScript discriminated unions prevent invalid states by enforcing explicit, mutually exclusive data shapes. Model data with a shared literal property across interfaces. This type-first approach catches unreachable states at compile time, preventing runtime errors before deployment.

Branded types are domain primitives that protect API boundaries by distinguishing structurally identical types at the compiler level. They prevent invalid assignments, ensuring data integrity by validating inputs at boundaries before processing.

Enforce exhaustive type handling during refactors by applying exhaustive type guards and runtime checks. This ensures all possible discriminated union cases are handled, surfacing unhandled states immediately as compiler errors.

No external tooling is required beyond standard TypeScript tooling. Turn on strict mode in tsconfig.json and model data explicitly. Optional libraries like Zod can enhance runtime validation at boundaries.

Validate runtime inputs by applying boundary checks using optional libraries like Zod. Define function signatures and contracts before implementation to validate inputs across frontend and backend TypeScript code safely.

TypeScript code fails at runtime when type-first development is misused, leading to unclear contracts and fragile code. Fix this by enforcing discriminated unions, branded types, and runtime validation across system boundaries.