typescript-expert

Generics let you create functions, interfaces, and classes that work with multiple types while preserving type safety. Define a generic parameter with angle brackets—for example, `function identity<T>(value: T): T`—then TypeScript enforces the same type on input and output, catching mismatches at compile time instead of runtime.

Discriminated unions combine a literal type field with type narrowing to model mutually exclusive states safely. For example, `type Result<T> = { status: 'success'; data: T } | { status: 'error'; error: string }` lets TypeScript automatically narrow which properties exist based on the `status` field, eliminating runtime type checks.

Mapped types transform existing types into new ones programmatically. Use `type Readonly<T> = { readonly [K in keyof T]: T[K] }` to derive a read-only version from any type, or construct permission or validation interfaces from a single source of truth, keeping large codebases maintainable as requirements evolve.

Yes. TypeScript's advanced type system—conditional types, utility types, and strict inference—enforces contracts between modules at compile time with zero runtime cost. Design APIs with precise generic constraints and discriminated unions so type mismatches fail during development, not in production.

No. Advanced type features—generics, conditional types, mapped types, and discriminated unions—are built into TypeScript's type system. You can model complex domains, enforce strong contracts, and create type-safe utilities and APIs entirely through the language itself without additional runtime dependencies.

Conditional types use `T extends U ? X : Y` syntax to compute output types based on input generics, scaling predictably for complex scenarios. Overloads require listing each signature separately. Conditional types reduce duplication, improve maintainability, and let TypeScript infer precise types automatically across library and application code.