TypeScript Advanced Patterns

Take your TypeScript skills to the next level.

Conditional Types

type IsString<T> = T extends string ? true : false;

type A = IsString<string>; // true
type B = IsString<number>; // false

Mapped Types

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

interface User {
  name: string;
  age: number;
}

type ReadonlyUser = Readonly<User>;

Template Literal Types

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

type ClickEvent = EventName<'click'>; // 'onClick'
type FocusEvent = EventName<'focus'>; // 'onFocus'

Type Guards

function isString(value: unknown): value is string {
  return typeof value === 'string';
}

if (isString(input)) {
  console.log(input.toUpperCase());
}

Utility Types

// Pick
type UserName = Pick<User, 'name'>;

// Omit
type UserWithoutAge = Omit<User, 'age'>;

// Partial
type PartialUser = Partial<User>;

Conclusion

Advanced TypeScript patterns enable more type-safe and expressive code.