typescript

Generics allow creating reusable components that work with multiple types while maintaining type safety. They use type parameters (like <T>) that are specified when the component is used, enabling type inference and constraints.

Type guards are runtime checks that narrow types within conditional blocks. Built-in guards include typeof, instanceof, and in operators. Custom type guards are functions returning a type predicate (param is Type) to narrow types based on custom logic.

Utility types are built-in generic types that transform other types. Common ones include Partial<T> (all optional), Required<T> (all required), Pick<T,K> (select properties), Omit<T,K> (exclude properties), and Record<K,V> (object type).

TypeScript supports ES6 modules with import/export syntax. Use 'import type' for type-only imports (erased at compile time). Declaration files (.d.ts) provide types for JavaScript libraries. Module resolution follows Node.js or bundler strategies.

Enums define named constants that can be numeric or string values. They exist at runtime as objects. Union types ('a' | 'b') are often preferred for string literals as they're lighter weight and better tree-shaken. Use enums when you need runtime access to values.