如何以编程方式枚举枚举类型？

Question 1

假设我有一个TypeScript enum，MyEnum如下所示：

enum MyEnum {
    First,
    Second,
    Third
}

TypeScript 0.9.5中生成enum值数组的最佳方法是什么？例：

var choices: MyEnum[]; // or Array<MyEnum>
choices = MyEnum.GetValues(); // plans for this?
choices = EnumEx.GetValues(MyEnum); // or, how to roll my own?

Question 2

这是该枚举的JavaScript输出：

var MyEnum;
(function (MyEnum) {
    MyEnum[MyEnum["First"] = 0] = "First";
    MyEnum[MyEnum["Second"] = 1] = "Second";
    MyEnum[MyEnum["Third"] = 2] = "Third";
})(MyEnum || (MyEnum = {}));

这是一个像这样的对象：

{
    "0": "First",
    "1": "Second",
    "2": "Third",
    "First": 0,
    "Second": 1,
    "Third": 2
}

带有字符串值的枚举成员

TypeScript 2.4增加了枚举可能具有字符串枚举成员值的功能。因此，可能会得到一个如下所示的枚举：

enum MyEnum {
    First = "First",
    Second = 2,
    Other = "Second"
}

// compiles to
var MyEnum;
(function (MyEnum) {
    MyEnum["First"] = "First";
    MyEnum[MyEnum["Second"] = 2] = "Second";
    MyEnum["Other"] = "Second";
})(MyEnum || (MyEnum = {}));

获取会员名称

我们可以看一下上面的示例，尝试弄清楚如何获取枚举成员：

{
    "2": "Second",
    "First": "First",
    "Second": 2,
    "Other": "Second"
}

这是我想出的：

const e = MyEnum as any;
const names = Object.keys(e).filter(k => 
    typeof e[k] === "number"
    || e[k] === k
    || e[e[k]]?.toString() !== k
);

会员价值

一旦有了名称，就可以通过以下操作遍历它们以获得相应的值：

const values = names.map(k => MyEnum[k]);

扩展类

我认为最好的方法是创建自己的函数（例如EnumEx.getNames(MyEnum)）。您不能向枚举添加函数。

class EnumEx {
    private constructor() {
    }

    static getNamesAndValues(e: any) {
        return EnumEx.getNames(e).map(n => ({ name: n, value: e[n] as string | number }));
    }

    static getNames(e: any) {
        return Object.keys(e).filter(k => 
            typeof e[k] === "number"
            || e[k] === k
            || e[e[k]]?.toString() !== k
        );
    }

    static getValues(e: any) {
        return EnumEx.getNames(e).map(n => e[n] as string | number);
    }
}

Question 3

使用TypeScript> = 2.4，您可以定义字符串枚举：

enum Color {
  RED = 'Red',
  ORANGE = 'Orange',
  YELLOW = 'Yellow',
  GREEN = 'Green',
  BLUE = 'Blue',
  INDIGO = 'Indigo',
  VIOLET = 'Violet'
}

JavaScript ES5输出：

var Color;
(function (Color) {
    Color["RED"] = "Red";
    Color["ORANGE"] = "Orange";
    Color["YELLOW"] = "Yellow";
    Color["GREEN"] = "Green";
    Color["BLUE"] = "Blue";
    Color["INDIGO"] = "Indigo";
    Color["VIOLET"] = "Violet";
})(Color || (Color = {}));

这是一个像这样的对象：

const Color = {
  "RED": "Red",
  "ORANGE": "Orange",
  "YELLOW": "Yellow",
  "GREEN": "Green",
  "BLUE": "Blue",
  "INDIGO": "Indigo",
  "VIOLET": "Violet"
}

因此，对于字符串枚举，无需过滤内容， Object.keys(Color)并且Object.values(Color)（*）就足够了：

const colorKeys = Object.keys(Color) as (keyof typeof Color)[];
console.log('colorKeys =', colorKeys);
// ["RED", "ORANGE", "YELLOW", "GREEN", "BLUE", "INDIGO", "VIOLET"]

const colorValues = Object.values(Color);
console.log('colorValues =', colorValues);
// ["Red", "Orange", "Yellow", "Green", "Blue", "Indigo", "Violet"]

colorKeys.map(colorKey => {
  console.log(`color key = ${colorKey}, value = ${Color[colorKey]}`);
});
/*
color key = RED, value = Red
color key = ORANGE, value = Orange
color key = YELLOW, value = Yellow
color key = GREEN, value = Green
color key = BLUE, value = Blue
color key = INDIGO, value = Indigo
color key = VIOLET, value = Violet
*/

在TypeScript游乐场上查看在线示例

（*）旧浏览器需要使用Polyfill，请参阅https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_objects/Object/values#Browser_compatibility

Question 4

您可以添加函数以获取枚举的名称和索引：

enum MyEnum {
  First,
  Second,
  Third
}

namespace MyEnum {
  function isIndex(key):boolean {
    const n = ~~Number(key);
    return String(n) === key && n >= 0;
  }

  const _names:string[] = Object
      .keys(MyEnum)
      .filter(key => !isIndex(key));

  const _indices:number[] = Object
      .keys(MyEnum)
      .filter(key => isIndex(key))
      .map(index => Number(index));

  export function names():string[] {
    return _names;
  }

  export function indices():number[] {
    return _indices;
  }
}

console.log("MyEnum names:", MyEnum.names());
// Prints: MyEnum names: ["First", "Second", "Third"]

console.log("MyEnum indices:", MyEnum.indices());
// Prints: MyEnum indices: [0, 1, 2]

请注意，您可以只导出_names和_indicesconst而不是通过导出的函数将其公开，但是由于导出的成员是枚举的成员，因此可以说将它们作为函数更清晰，因此它们不会与实际的枚举成员混淆。

如果TypeScript为所有枚举自动生成类似这样的东西，那就太好了。

Question 5

在TypeScript（认为：反射）中没有RTTI（运行时类型信息）的概念，因此，为了做到这一点，需要了解已转译的JavaScript。因此，假设TypeScript 0.95：

enum MyEnum {
    First, Second, Third
}

变成：

var MyEnum;
(function(MyEnum) {
    MyEnum[MyEnum["First"] = 0] = "First";
    MyEnum[MyEnum["Second"] = 1] = "Second";
    MyEnum[MyEnum["Third"] = 2] = "Third";
}

因此，这被建模为javascript中的常规对象，其中MyEnum.0 == "First"和MyEnum.First == 0。因此，要枚举所有枚举名称，您需要获取属于该对象且不是数字的所有属性：

for (var prop in MyEnum) {         
    if (MyEnum.hasOwnProperty(prop) &&
        (isNaN(parseInt(prop)))) {
        console.log("name: " + prop);
    }
}

好的，所以现在我告诉你了如何做，我被允许告诉你这是一个坏主意。您不是在编写托管语言，所以您无法养成这些习惯。它仍然只是普通的旧JavaScript。如果我想使用JavaScript中的结构来填充某种选择列表，则可以使用普通的旧数组。双关语意在此，枚举不是正确的选择。TypeScript的目标是生成惯用的漂亮JavaScript。以这种方式使用枚举不会保留此目标。

Question 6

我使用了David Sherret提出的解决方案，并编写了一个npm库，您可以使用named enum-values...

Git：枚举值

// Suppose we have an enum
enum SomeEnum {
  VALUE1,
  VALUE2,
  VALUE3
}

// names will be equal to: ['VALUE1', 'VALUE2', 'VALUE3']
var names = EnumValues.getNames(SomeEnum);

// values will be equal to: [0, 1, 2]
var values = EnumValues.getValues(SomeEnum);

Question 7

单行获取条目列表（键值对象/对）：

Object.keys(MyEnum).filter(a=>a.match(/^\D/)).map(name=>({name, value: MyEnum[name] as number}));

Question 8

enum MyEnum {
    First, Second, Third, NUM_OF_ENUMS
}

for(int i = 0; i < MyEnum.NUM_OF_ENUMS; ++i) {
    // do whatever you need to do.
}

Question 9

如果要将字符串值与枚举关联，则这些方法无效。要具有通用功能，您可以执行以下操作：

function listEnum(enumClass) {
    var values = [];
    for (var key in enumClass) {
        values.push(enum[key]);
    }
    values.length = values.length / 2;
    return values;
}

之所以可行，是因为TypeScript将在第一步中添加键，并在第二步中添加值。

在TypeScript中，它是：

var listEnums = <T> (enumClass: any): T[]=> {
    var values: T[] = [];
    for (var key in enumClass) {
        values.push(enumClass[key]);
    }
    values.length = values.length / 2;
    return values;
};

var myEnum: TYPE[] = listEnums<TYPE>(TYPE);

Question 10

joe的回答使我意识到，依赖前N个数字键比进行更复杂的测试要容易得多：

function getEnumMembers(myEnum): string[]
{
    let members = []
    for(let i:number = 0; true; i++) {
        if(myEnum[i] === undefined) break
        members.push(myEnum[i])
    }

    return members
}

enum Colors {
    Red, Green, Blue
}

console.log(getEnumMembers(myEnum))

Question 11

对于nodejs：

const { isNumber } = require('util');

Object.values(EnumObject)
      .filter(val => isNumber(val))
      .map(val => {
         // do your stuff
      })

Question 12

遍历一个枚举

字符串枚举最好用于此目的。这是一个例子：

// This is a string enum
enum MyEnum {
    First = 'First',
    Second = 'Second',
    Third = 'Third',
}

// An enum is a TS concept
// However his MyEnum compiles to JS object:
//  {
//   "First": "First",
//   "Second": "Second",
//   "Third": "Third"
// } 


// Therefore we can get the keys in the following manner:
const keysArray = Object.keys(MyEnum);

for (const key of keysArray) {
    console.log(key)
}
// [LOG]: "First" 
// [LOG]: "Second" 
// [LOG]: "Third"