Advanced TypeScript Patterns

TypeScript offers powerful type-level programming capabilities that can help you write more robust and maintainable code.

Conditional Types

Conditional types allow you to create types that depend on a condition:

type NonNullable<T> = T extends null | undefined ? never : T;

type ApiResponse<T> = T extends string 
  ? { message: T } 
  : { data: T };

type StringResponse = ApiResponse<string>; 
type UserResponse = ApiResponse<User>;

Note: TypeScript's type system is Turing complete, meaning you can perform complex computations at the type level.

Mapped Types

Transform existing types by mapping over their properties:

type Partial<T> = {
  [P in keyof T]?: T[P];
};

type Required<T> = {
  [P in keyof T]-?: T[P];
};

type Readonly<T> = {
  readonly [P in keyof T]: T[P];
};

Template Literal Types

Create new string literal types:

type EventName<T extends string> = `on${Capitalize<T>}`;

type MouseEvents = EventName<'click' | 'hover' | 'focus'>;

type CSSProperty = `--${string}`;
type CSSValue = CSSProperty | 'inherit' | 'initial';

These patterns help create more expressive and type-safe APIs.