前言

在当前的javascript中，并没有枚举这个概念，在某些场景中使用枚举更能保证数据的正确性，减少数据校验过程，下面就介绍一下javascript如何模拟实现枚举效果。

枚举主要特点

1. 枚举值不能重复
2. 不能被修改

实现

let days;
(function (days) {
    days[days["Sunday"] = 0] = "Sunday";
    days[days["Monday"] = 1] = "Monday";
    days[days["Tuesday"] = 2] = "Tuesday";
    days[days["Wednesday"] = 3] = "Wednesday";
    days[days["Thursday"] = 4] = "Thursday";
    days[days["Friday"] = 5] = "Friday";
    days[days["Saturday"] = 6] = "Saturday";
})(days || (days = {}));

这个时候days对象基本实现了枚举效果，可以通过枚举值或索引去访问days对象，但枚举有个重要特别是不能被修改，这个时候days是可以随意修改的；可以通过Object.freeze函数让对象不改修改，重新导出一个不可以修改的对象，完整代码如下：

let days;
(function (days) {
    days[days["Monday"] = 1] = "Monday";
    days[days["Tuesday"] = 2] = "Tuesday";
    days[days["Wednesday"] = 3] = "Wednesday";
    days[days["Thursday"] = 4] = "Thursday";
    days[days["Friday"] = 5] = "Friday";
    days[days["Saturday"] = 6] = "Saturday";
    days[days["Sunday"] = 0] = "Sunday";
})(days || (days = {}));

//导出可枚举对象
export EnumWeek = Object.freeze(days)

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