javascript - 为什么 TypeScript 转译器将枚举编译成字典查找而不是简单的对象？

Question

我很好奇为什么 TypeScript 转译器将枚举编译成字典查找而不是简单的对象。这是一个 TypeScript 枚举示例:

enum transactionTypesEnum {
    None = 0,

    OSI = 4, 
    RSP = 5,
    VSP = 6,
    SDIV = 7,
    CDIV = 8
}

这是 TypeScript 发出的 JS 代码:

var TransactionTypes;
(function (TransactionTypes) {
    TransactionTypes[TransactionTypes["None"] = 0] = "None";
    TransactionTypes[TransactionTypes["OSI"] = 4] = "OSI"; 
    TransactionTypes[TransactionTypes["RSP"] = 5] = "RSP"; 
    TransactionTypes[TransactionTypes["VSP"] = 6] = "VSP"; 
    TransactionTypes[TransactionTypes["SDIV"] = 7] = "SDIV";
    TransactionTypes[TransactionTypes["CDIV"] = 8] = "CDIV";
})(TransactionTypes || (TransactionTypes = {}));

我的好奇心是想知道为什么 TypeScript 不简单地这样做:

var TransactionTypes = {
    None: 0,
    OSI: 4,
    RSP: 5,
    VSP: 6,
    SDIV: 7,
    CDIV: 8
}

Answer 1

TypeScript enum 类型提供安全的双向映射，因此您可以根据以下所有内容获取名称或值(例如获取值、从值中获取名称以及来自纯字符串的值)

enum Musketeers {
  CAV = 0,
  BAS = 1,
  USR = 2
}

const selection = Musketeers.BAS;

// 1
console.log(selection);

const selectionName = Musketeers[selection];

// BAS
console.log(selectionName);

const fromString = Musketeers['BAS'];

// 1
console.log(fromString);

特别是字典不支持这一行(无需编写额外的代码):

// Gets the name from the value
const selectionName = Musketeers[1];