📘

Mapped Types: Transforming Types

Advanced

130 XP

50 min

Lesson Content

Mapped Types

Mapped types allow you to create new types by transforming properties of existing types.

Basic Mapped Type

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

type ReadonlyUser = Readonly;

Modifiers

// Remove readonly
type Writable = {
  -readonly [P in keyof T]: T[P];
};

// Remove optional
type Required = {
  [P in keyof T]-?: T[P];
};

Key Remapping

type Getters = {
  [K in keyof T as `get${Capitalize}`]: () => T[K];
};

Example Code

Understanding mapped type transformations

// Mapped types work at compile time
// For practice, simulate property transformation

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

// Simulate making all properties optional
function makeOptional(obj: User): Partial<User> {
  return obj;
}

const user: Partial<User> = makeOptional({ name: "John", age: 30 });
console.log(user);

Expected Output:

{ name: 'John', age: 30 }

Study Tips

•Read the theory content thoroughly before practicing
•Review the example code to understand key concepts
•Proceed to the Practice tab when you're ready to code