枚举进阶

1. 枚举类型

// 数字枚举
enum Direction {
  Up,
  Down,
  Left,
  Right,
}

// 字符串枚举
enum Status {
  Active = 'ACTIVE',
  Inactive = 'INACTIVE',
}

// 异构枚举（不推荐）
enum BooleanLike {
  No = 0,
  Yes = 'YES',
}

2. const 枚举

const enum Colors {
  Red = '#FF0000',
  Green = '#00FF00',
  Blue = '#0000FF',
}

let color = Colors.Red; // 编译为 '#FF0000'

3. 枚举与类型

// 枚举成员类型
enum ShapeKind {
  Circle,
  Square,
}

interface Circle {
  kind: ShapeKind.Circle;
  radius: number;
}
interface Square {
  kind: ShapeKind.Square;
  size: number;
}

type Shape = Circle | Square;

// 枚举合并
enum Weekday {
  Mon,
  Tue,
  Wed,
}
enum Weekday {
  Thu = 3,
  Fri,
  Sat,
  Sun,
}

4. 枚举替代方案

// as const 对象
const Direction = {
  Up: 'UP',
  Down: 'DOWN',
  Left: 'LEFT',
  Right: 'RIGHT',
} as const;

type Direction = (typeof Direction)[keyof typeof Direction];
// 'UP' | 'DOWN' | 'LEFT' | 'RIGHT'

// 联合类型
type Status = 'active' | 'inactive' | 'pending';

// 辅助函数
function enumFromObj<T extends Record<string, string>>(obj: T) {
  return { ...obj, values: Object.values(obj) as T[keyof T][] };
}