TypeScript枚举Enum的具体使用

enum StatusCode { Success = 200, NotFound = 404 }
if (response.status === StatusCode.Success) { ... } // 比直接判断200更清晰

enum Direction { Up, Down }
let dir: Direction = Direction.Up; // 正确
dir = 3; // 错误：不能将数字直接赋值给枚举类型

enum LogLevel { Info, Warn, Error }

enum Direction {
  Up = 1,     // 显式赋值
  Down,       // 自动递增为2
  Left = 4,
  Right,      // 自动递增为5
}
console.log(Direction.Down);    // 输出: 2
console.log(Direction[2]);      // 输出: "Down"（反向映射）

enum LogLevel {
  Info = "INFO",
  Warn = "WARN",
  Error = "ERROR"
}
console.log(LogLevel.Info); // 输出: "INFO"

const enum Size { Small, Medium }
let size = Size.Small; // 编译后：let size = 0;

enum BooleanLikeEnum {
  No = 0,
  Yes = "YES",
}

enum Foo {
  A,
}
enum Foo {
  B = 1,
}
enum Foo {
  C = 2,
}
// 等同于
enum Foo {
  A,
  B = 1，
  C = 2
}

enum FileAccess {
  None,                   // 常量成员 0
  Read = 1 << 1,          // 计算成员 2
  Write = 1 << 2,         // 计算成员 4
  ReadWrite = Read | Write, // 计算成员 6
  // 后续成员必须显式初始化
  Execute = 8
}

enum UserRole { Admin, Guest }
function setRole(role: UserRole) { ... }
setRole(UserRole.Admin); // 正确
setRole(2); // 错误：类型不符

enum Operator {
  ADD,
  DIV,
  MUL,
  SUB
}
function compute(
  op:Operator,
  a:number,
  b:number
) {
  switch (op) {
    case Operator.ADD:
      return a + b;
    case Operator.DIV:
      return a / b;
    case Operator.MUL:
      return a * b;
    case Operator.SUB:
      return a - b;
    default:
      throw new Error('wrong operator');
  }
}
compute(Operator.ADD, 1, 3) // 4

enum Theme { Dark = 'dark', Light = 'light' }
function setTheme(theme: Theme) { ... }
setTheme(Theme.Dark);

type Theme = 'dark' | 'light';
function setTheme(theme: Theme) { ... }
setTheme('dark');