typescript-type-safety

Type safety in TypeScript eliminates `any` by using type guards, branded types, and discriminated unions to narrow unknown values at compile time. Implement custom type predicates to safely handle unknown data, create branded types for domain-specific primitives like `UserId`, and use discriminated unions for exhaustive type-checking, catching errors before runtime.

Type guards are custom predicates that narrow `unknown` types to specific interfaces through runtime checks. Define a type predicate function that validates properties and returns `value is TargetType`, then use it in conditionals to safely access typed properties. This ensures type-safe access without casting to `any`.

Discriminated unions use a shared literal property to distinguish between union members, enabling exhaustive type-checking with `switch` statements. TypeScript narrows the type based on the discriminator, forcing you to handle all cases and preventing accessing properties that don't exist on a particular union member.

Branded types create distinct types from primitives by adding a nominal identity, preventing accidental assignment between similar values. For example, create `OrderId` and `UserId` as distinct branded types so functions expecting `OrderId` reject `UserId` arguments, catching logic errors at compile time.

Conditional types enable dynamic type computation based on conditions, while mapped types transform existing types systematically. Together they allow precise type narrowing and reliable interfaces by computing exact types for specific contexts, reducing the need for broad `any` or `unknown` casts.

Type safety fundamentals like type guards and branded types are accessible with intermediate TypeScript knowledge. Advanced patterns like conditional and mapped types deepen type precision but are optional; start with type guards and discriminated unions to eliminate `any`, then adopt advanced features as your domain modeling needs grow.