Typescript Advanced Types

Advanced TypeScript Types

Implementing advanced TypeScript type patterns — from conditional and mapped types through template literals, infer, and type-level programming.

When to Use

• Building type-safe TypeScript libraries
• Implementing complex type transformations
• Generic utility types
• Type-level validation and parsing

TypeScript Type Patterns

// Conditional types with infer
type UnpackPromise<T> = T extends Promise<infer U> ? U : T;
type Result = UnpackPromise<Promise<string>>; // string

// Mapped types with key remapping
type Getters<T> = {
  [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K]
};

// Template literal types
type EventName<T extends string> = `on${Capitalize<T>}`;
type ClickEvent = EventName<'click'>; // 'onClick'

// Discriminated union pattern
type ApiResult<T> = 
  | { status: 'success'; data: T }
  | { status: 'error'; error: string }
  | { status: 'loading' };

Verification Checklist

• Conditional types with infer for unwrapping
• Mapped types with key remapping and filtering
• Template literal types for string manipulation
• Recursive type aliases
• Discriminated unions for state modeling
• satisfies operator for type validation (TS 4.9+)