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 动态添加属性。当我们调用 Direction.Up 发生了什么？
Direction["Up"] = 1 这个不难理解
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) //1
console.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 有所了解了吧，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
也可以创建枚举时不给初始值
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;
}
