08-enums.ts

// ============================================
// 08. Enums
// ============================================

// Numeric Enums - default behavior
enum Direction {
  Up,      // 0
  Down,    // 1
  Left,    // 2
  Right   // 3
}

let direction: Direction = Direction.Up;
console.log(direction); // 0

// Custom Numeric Values
enum Status {
  Pending = 1,
  Approved = 2,
  Rejected = 3
}

// Or start from a specific number
enum Status2 {
  Pending = 100,
  Approved,    // 101
  Rejected     // 102
}

// String Enums
enum Color {
  Red = "red",
  Green = "green",
  Blue = "blue"
}

let color: Color = Color.Red;
console.log(color); // "red"

// Heterogeneous Enums (not recommended)
enum Mixed {
  No = 0,
  Yes = "yes"
}

// Computed and Constant Members
enum FileAccess {
  None,           // 0 (constant)
  Read = 1 << 1,  // 2 (computed)
  Write = 1 << 2, // 4 (computed)
  ReadWrite = Read | Write // 6 (computed)
}

// const Enums - inlined at compile time
const enum DirectionConst {
  Up,
  Down,
  Left,
  Right
}

let directionConst = DirectionConst.Up;
// Compiles to: let directionConst = 0;

// Reverse Mapping (numeric enums only)
enum DirectionReverse {
  Up = 1,
  Down,
  Left,
  Right
}

console.log(DirectionReverse.Up);        // 1
console.log(DirectionReverse[1]);        // "Up" (reverse mapping)

// String enums don't have reverse mapping
// Color["red"]; // undefined

// Common Use Cases

// HTTP Status Codes
enum HttpStatus {
  OK = 200,
  NotFound = 404,
  ServerError = 500
}

// API Response Codes
enum ApiResponse {
  Success = "SUCCESS",
  Error = "ERROR",
  Pending = "PENDING"
}

// Flags/Bitwise operations
enum Permission {
  Read = 1,
  Write = 2,
  Execute = 4
}

const userPermissions = Permission.Read | Permission.Write;
console.log(userPermissions & Permission.Read); // 1 (has read permission)

export { Direction, Status, Color, HttpStatus, ApiResponse, Permission };