typescript - ts的枚举实现代码什么意思？

Question

var Days;(function (Days) {    Days[Days["Sun"] = 0] = "Sun";    Days[Days["Mon"] = 1] = "Mon";    Days[Days["Tue"] = 2] = "Tue";    Days[Days["Wed"] = 3] = "Wed";    Days[Days["Thu"] = 4] = "Thu";    Days[Days["Fri"] = 5] = "Fri";    Days[Days["Sat"] = 6] = "Sat";})(Days || (Days = {}));

Answer 1

枚举包含七个成员，表示从星期日到星期六,每个都有对应的数字，例如 Sun 的值是 0，Mon 的值是 1
使用:

const today: Days = Days.Wed; // 将今天设定为星期三if (today === Days.Wed) {    console.log("今天是星期三！");} else {    console.log("今天不是星期三。");}

Answer 2

枚举编译后就是一个普通对象，只是这些键值有一个反向映射。

const Days = {}Days[0] = 'Sun'Days.Sun = 0

Answer 3

就是KV双向映射，Days既可以Days.Sun获取到枚举值0，也可以反向Days[Days.Sun]获取到"Sun"这个枚举值0对应的key，就是方便你获取key和value；具体到JS代码上就是知道赋值语句本身也有返回值就能理解了，就是比如Days["Sun"] = 0]这条赋值语句执行后的结果也是有返回值的，返回值就是赋值的那个值，相当于将通常是两行代码的语句糅合成一条，等价于Days["Sun"] = 0; Days[0] = "Sun";