How do you write reusable code in TypeScript that works with different types?

Generics in TypeScript are a way to create reusable components that work with a variety of types rather than a single one. They allow you to capture the type a user provides so that it can be used later, enabling type-safe code that doesn't sacrifice flexibility.

The most common use case is with functions. Instead of using 'any' (which loses type information), you can use a generic type parameter: function identity<T>(arg: T): T { return arg; }. When you call this function, TypeScript infers the type or you can explicitly specify it.

Generics are extensively used in: container types (Array<T>, Map<K, V>), utility types (Partial<T>, Pick<T, K>), async operations (Promise<T>), and React components (FC<Props>). They allow libraries to provide type-safe APIs without knowing the specific types users will provide.

You can constrain generics using extends: <T extends object> ensures T is an object type. You can use multiple type parameters (<T, K extends keyof T>) and provide default types (<T = string>). Understanding generics is essential for writing reusable TypeScript code and understanding library type definitions.