Typescript 中枚举（上）

可以在初始化枚举时对 Up 赋值，枚举好处是给我们一种不可以修改的集合可以用来作为配置选项，我们无法在随后动态修改

enum Direction {    Up = 1,    Down,    Left,    Right,}

这是枚举编译后的 js 文件，

编译后的枚举

var Direction;(function (Direction) {    Direction[Direction["Up"] = 1] = "Up";    Direction[Direction["Down"] = 2] = "Down";    Direction[Direction["Left"] = 3] = "Left";    Direction[Direction["Right"] = 4] = "Right";})(Direction || (Direction = {}));

var Direction;(function (Direction) {    Direction[Direction["Up"] = 1] = "Up";    Direction[Direction["Down"] = 2] = "Down";    Direction[Direction["Left"] = 3] = "Left";    Direction[Direction["Right"] = 4] = "Right";})(Direction || (Direction = {}));Direction.OK = 1;console.log(Direction.Up)console.log(Direction.OK)

我们是可以为 Direction 动态增加属性。当我们调用 Direction.Up 发生了什么？
Direction[“Up”] = 1 这个不难了解

var obj = {};// obj["Up"] = 1;obj[obj["Up"] = 1]console.log(obj.Up) //1

// obj["Up"] = 1;obj[obj["Up"] = 1] = "Up"console.log(obj.Up)console.log(obj.Up = 1) //1console.log(obj[1]) // Up

通过上面代码解释我们大家可能为 typescript 如何实现 enum 有所理解了吧，大家可以在自己 js 项目这样来定义您的枚举结构。

无初始化的枚举

也可以创立枚举时不给初始值

enum Direction {    Up,    Down,    Left,    Right,}

枚举的调用

enum Response {    No = 0,    Yes = 1,}function respond(recipient: string, message: Response): void {    // ...}respond("Princess Caroline", Response.Yes)

调用枚举也很简单，就像调用对象属性一样简单。

枚举的表达式赋值

enum E{    A = getSomeValue(),    B // error! 'A' 是表达式初始化而不是固定值所以 'B' 需要初始化     }function getSomeValue(){    return 1;}

enum E{    A = getSomeValue(),    B = getSomeValue()    }function getSomeValue(){    return 1;}