從帶有字符串的 Typescript 枚舉中獲取值

Question

我試圖從這個枚舉中獲取值：

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

使用其他 StackOverflows 中建議的以下代碼，我得到以下輸出：

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

console.log(text);

---

Tiny
VerySmall
Very Small
Small
Medium
Large
VeryLarge
Very Large

我不想要非常小的和非常大的條目，為什么會出現這些條目，我怎樣才能得到我想要的結果？

謝謝！

Answer 1

看起來正在使用的打字稿編譯器是 2.4 之前的，他們在枚舉中添加了字符串值支持。 通常存在從值到枚舉的反向映射，並且值通常是數字。 但是，如果您嘗試使用 2.4 之前的字符串，編譯器將不知道如何處理它（並且實際上會產生錯誤），但仍會生成源代碼。

比較 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 = {}));

到 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 = {}));

和 2.3 沒有字符串值：

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 = {}));

如果您想在 2.4 及更高版本中強制進行反向映射，您可以將值斷言為any 。

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

只需將其稱為功能即可。

Answer 2

在 TypeScript 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();

記住 for-In 應該有一個 if-Statement！

兩個console.log(text) ，都應該輸出相同的字符串。

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

如果您登錄Sizes[size]后安慰了，你會想到什么發生，為什么你得到的值。

Answer 3

您可以使用Object.keys獲取枚舉鍵並記錄值，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]);
}

輸出：

Tiny
Very Small
Small
Medium
Large
Very Large

轉譯示例：

 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]); }