为什么枚举会转换为函数？

考虑：

enum Colors {
    Red,
    Green,
    Blue
}

它转换成这样：

var Colors;
(function (Colors) {
    Colors[Colors["Red"] = 0] = "Red";
    Colors[Colors["Green"] = 1] = "Green";
    Colors[Colors["Blue"] = 2] = "Blue";
})(Colors || (Colors = {}));

关于此结果的大多数问题都在TypeScript 中的枚举：JavaScript 代码在做什么？ https://stackoverflow.com/questions/20278095/enums-in-typescript-what-is-the-javascript-code-doing.

我引用一下答案：

这是一个“立即执行的函数”

并进一步深入主题：

认为他们可能会去：

var Colors;
Colors || (Colors = {});
Colors[Colors["Cyan"] = 3] = "Cyan";
// ...

并跳过关闭，但也许我仍然遗漏了一些东西。

所以问题仍然存在：为什么将其包装在立即执行的函数中？

我相信 TypeScript 使用 IIFE（又名立即调用函数表达式），因为变量名称可以缩小。如果您的枚举名称很长，例如MySuperAmazingStatesNeededForWhateverIWantEnum，它可以在 IIFE 中缩小为只有一个字母

// amazing_enum.js
var MySuperAmazingStatesNeededForWhateverIWantEnum;
(function MySuperAmazingStatesNeededForWhateverIWantEnum() {
    MySuperAmazingStatesNeededForWhateverIWantEnum[MySuperAmazingStatesNeededForWhateverIWantEnum["Red"] = 0] = "Red";
    MySuperAmazingStatesNeededForWhateverIWantEnum[MySuperAmazingStatesNeededForWhateverIWantEnum["Green"] = 1] = "Green";
    MySuperAmazingStatesNeededForWhateverIWantEnum[MySuperAmazingStatesNeededForWhateverIWantEnum["Blue"] = 2] = "Blue";
})(MySuperAmazingStatesNeededForWhateverIWantEnum || (MySuperAmazingStatesNeededForWhateverIWantEnum = {}));

// amazing_enum.min.js
var MySuperAmazingStatesNeededForWhateverIWantEnum;!function e(){e[e.t=0]="Red",e[e.u=1]="Green",e[e.m=2]="Blue"}(MySuperAmazingStatesNeededForWhateverIWantEnum||(MySuperAmazingStatesNeededForWhateverIWantEnum={}));

如果没有 IIFE 缩小就不会那么有效

// amazing_enum.js
var MySuperAmazingStatesNeededForWhateverIWantEnum;
MySuperAmazingStatesNeededForWhateverIWantEnum || (MySuperAmazingStatesNeededForWhateverIWantEnum = {}),
MySuperAmazingStatesNeededForWhateverIWantEnum[MySuperAmazingStatesNeededForWhateverIWantEnum.Red = 0] = "Red";
MySuperAmazingStatesNeededForWhateverIWantEnum[MySuperAmazingStatesNeededForWhateverIWantEnum.Green = 1] = "Green";
MySuperAmazingStatesNeededForWhateverIWantEnum[MySuperAmazingStatesNeededForWhateverIWantEnum.Blue = 2] = "Blue";

// amazing_enum.min.js
var MySuperAmazingStatesNeededForWhateverIWantEnum;MySuperAmazingStatesNeededForWhateverIWantEnum||(MySuperAmazingStatesNeededForWhateverIWantEnum={}),MySuperAmazingStatesNeededForWhateverIWantEnum[MySuperAmazingStatesNeededForWhateverIWantEnum.t=0]="Red",MySuperAmazingStatesNeededForWhateverIWantEnum[MySuperAmazingStatesNeededForWhateverIWantEnum.u=1]="Green",MySuperAmazingStatesNeededForWhateverIWantEnum[MySuperAmazingStatesNeededForWhateverIWantEnum.m=2]="Blue";

大小差异很大。