Question

我正在尝试从该枚举中获取值：

zed <- zed %>% 
  dplyr::mutate(newCol = ifelse(possessionName[2:length(possessionName)] != possessionName[1:(length(possessionName)-1)], 1, 0))

使用其他StackOverflows中建议的以下代码，我得到以下输出：

enum Sizes {
  Tiny = "Tiny",
  VerySmall = "Very Small",
  Small = "Small",
  Medium = "Medium",
  Large = "Large",
  VeryLarge = "Very Large"
}

var text=""
for (var size in Sizes) {
    text = text + "\n" + size;
}

console.log(text);

我不希望输入VerySmall和VeryLarge，为什么会出现这些以及如何获得所需的结果？

谢谢！

Answer 1

似乎正在使用的Typescript编译器是2.4之前的版本，它们在枚举中添加了字符串值支持。通常，从值到枚举存在反向映射，并且值通常是数字。但是，如果您尝试使用2.4之前的字符串，则编译器将不知道如何处理（实际上会产生错误），但仍会生成源代码。

比较2.4：

var Sizes;
(function (Sizes) {
    Sizes["Tiny"] = "Tiny";
    Sizes["VerySmall"] = "Very Small";
    Sizes["Small"] = "Small";
    Sizes["Medium"] = "Medium";
    Sizes["Large"] = "Large";
    Sizes["VeryLarge"] = "Very Large";
})(Sizes || (Sizes = {}));

至2.3：

var Sizes;
(function (Sizes) {
    Sizes[Sizes["Tiny"] = "Tiny"] = "Tiny";
    Sizes[Sizes["VerySmall"] = "Very Small"] = "VerySmall";
    Sizes[Sizes["Small"] = "Small"] = "Small";
    Sizes[Sizes["Medium"] = "Medium"] = "Medium";
    Sizes[Sizes["Large"] = "Large"] = "Large";
    Sizes[Sizes["VeryLarge"] = "Very Large"] = "VeryLarge";
})(Sizes || (Sizes = {}));

2.3没有字符串值：

var Sizes;
(function (Sizes) {
    Sizes[Sizes["Tiny"] = 0] = "Tiny";
    Sizes[Sizes["VerySmall"] = 1] = "VerySmall";
    Sizes[Sizes["Small"] = 2] = "Small";
    Sizes[Sizes["Medium"] = 3] = "Medium";
    Sizes[Sizes["Large"] = 4] = "Large";
    Sizes[Sizes["VeryLarge"] = 5] = "VeryLarge";
})(Sizes || (Sizes = {}));

如果要在2.4及更高版本中强制执行反向映射，可以将值声明为any。

enum Sizes {
  Tiny = <any>"Tiny",
  VerySmall = <any>"Very Small",
  Small = <any>"Small",
  Medium = <any>"Medium",
  Large = <any>"Large",
  VeryLarge = <any>"Very Large"
}

只需将其称为功能即可。

Answer 2

在TypeScrit中


enum Sizes {
  Tiny = "Tiny",
  VerySmall = "Very Small",
  Small = "Small",
  Medium = "Medium",
  Large = "Large",
  VeryLarge = "Very Large"
}
class Test {
  constructor() {
    let text = '';

    for (const key in Sizes) {
      if (Sizes.hasOwnProperty(key)) {
        text += Sizes[key] + '<br/>';
      }
    }
    console.log(text);

    text = '';
    Object.keys(Sizes).map(key => text += Sizes[key] + '<br/>');
    console.log(text);
  }
}
let t = new Test();

请记住，for-In应该具有if-Statement！

console.log(text)都应输出相同的字符串。

Tiny<br/>Very Small<br/>Small<br/>Medium<br/>Large<br/>Very Large<br/>

如果在for-In之后登录Sizes[size]进行控制台，您将想象what发生了，并且why得到了值。

Answer 3

您可以使用Object.keys获取枚举键并记录值，如下所示：

enum Sizes {
  Tiny = "Tiny",
  VerySmall = "Very Small",
  Small = "Small",
  Medium = "Medium",
  Large = "Large",
  VeryLarge = "Very Large"
}

for (const size of Object.keys(Sizes)) {
    console.log(Sizes[size]);
}

输出：

Tiny
Very Small
Small
Medium
Large
Very Large

已翻译的示例：

var Sizes;
(function (Sizes) {
    Sizes["Tiny"] = "Tiny";
    Sizes["VerySmall"] = "Very Small";
    Sizes["Small"] = "Small";
    Sizes["Medium"] = "Medium";
    Sizes["Large"] = "Large";
    Sizes["VeryLarge"] = "Very Large";
})(Sizes || (Sizes = {}));
for (var _i = 0, _a = Object.keys(Sizes); _i < _a.length; _i++) {
    var size = _a[_i];
    console.log(Sizes[size]);
}

使用字符串从Typescript枚举获取值

3 个答案: