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Enums

class

Enums define a set of named constants. Numeric enums auto-increment; string enums are explicit.

Syntax

enum Direction { Up, Down, Left, Right }

Example

javascript

// Numeric enum
enum Direction {
    Up    = 0,
    Down  = 1,
    Left  = 2,
    Right = 3,
}
console.log(Direction.Up);    // 0
console.log(Direction[0]);    // 'Up'

// String enum (preferred — no reverse mapping)
enum Status {
    Active   = 'ACTIVE',
    Inactive = 'INACTIVE',
    Pending  = 'PENDING',
}

const userStatus: Status = Status.Active;

Union & Intersection types

Partial<T> / Required<T>