typescript-advanced-types

Generics let you parameterize types, like `function identity<T>(value: T): T`, so one function works with many types while preserving type information. Add constraints with `extends` (e.g., `T extends HasLength`) to require specific properties on the type parameter.

Conditional types use the form `T extends U ? X : Y` to select a type based on a condition. The `infer` keyword extracts a type inside the condition, such as `type ReturnType<T> = T extends (...args: any[]) => infer R ? R : never`.

Mapped types are the syntax `{ [P in keyof T]: T[P] }` for transforming object types, while utility types like Partial, Pick, and Omit are built-in mapped types provided by TypeScript. You can write custom mapped types with key remapping using `as` for filtering or renaming properties.

No, TypeScript types are erased at compile time and provide no runtime guarantees. For runtime safety, combine types with type guards, assertion functions, or validation logic that checks values during execution.

Deeply nested conditional types and recursive type definitions force the compiler to evaluate many type branches, increasing check time. Mitigate this by simplifying types, caching computed types in aliases, and limiting recursion depth.

Use `unknown` whenever a value's type is not yet determined, because it forces explicit narrowing through type guards before use. Unlike `any`, which disables type checking entirely, `unknown` preserves compile-time safety.