如何在 TypeScript 中将字符串转换为枚举？

How do I convert a string to enum in TypeScript?

提问by Amitabh

I have defined the following enum in TypeScript:

我在 TypeScript 中定义了以下枚举：

enum Color{
    Red, Green
}

Now in my function I receive color as a string. I have tried the following code:

现在在我的函数中，我将颜色作为字符串接收。我尝试了以下代码：

var green= "Green";
var color : Color = <Color>green; // Error: can't convert string to enum

How can I convert that value to an enum?

如何将该值转换为枚举？

回答by basarat

Enums in TypeScript 0.9 are string+number based. You should not need type assertion for simple conversions:

TypeScript 0.9 中的枚举是基于字符串+数字的。对于简单的转换，您不应该需要类型断言：

enum Color{
    Red, Green
}

// To String
 var green: string = Color[Color.Green];

// To Enum / number
var color : Color = Color[green];

Try it online

网上试试

I have documention about this and other Enum patterns in my OSS book : https://basarat.gitbook.io/typescript/type-system/enums

我在我的 OSS 书中有关于这个和其他枚举模式的文档：https: //basarat.gitbook.io/typescript/type-system/enums

回答by Victor

As of Typescript 2.1 string keys in enums are strongly typed. keyof typeofis used to get info about available string keys (1):

从 Typescript 2.1 开始，枚举中的字符串键是强类型的。keyof typeof用于获取有关可用字符串键 ( 1) 的信息：

enum Color{
    Red, Green
}

let typedColor: Color = Color.Green;
let typedColorString: keyof typeof Color = "Green";

// Error "Black is not assignable ..." (indexing using Color["Black"] will return undefined runtime)
typedColorString = "Black";

// Error "Type 'string' is not assignable ..." (indexing works runtime)
let letColorString = "Red";
typedColorString = letColorString;

// Works fine
typedColorString = "Red";

// Works fine
const constColorString = "Red";
typedColorString = constColorString

// Works fine (thanks @SergeyT)
let letColorString = "Red";
typedColorString = letColorString as keyof typeof Color;

typedColor = Color[typedColorString];

https://www.typescriptlang.org/docs/handbook/advanced-types.html#index-types

https://www.typescriptlang.org/docs/handbook/advanced-types.html#index-types

回答by Artru

If you are sure that an input string has an exact match with Color enum then use:

如果您确定输入字符串与 Color 枚举完全匹配，请使用：

const color: Color = (<any>Color)["Red"];

In the case where an input string may not match Enum, use:

如果输入字符串可能与 Enum 不匹配，请使用：

const mayBeColor: Color | undefined = (<any>Color)["WrongInput"];
if (mayBeColor !== undefined){
     // TypeScript will understand that mayBeColor is of type Color here
}

Playground

操场

---

---

If we do not cast enumto <any>type then TypeScript will show the error:

如果我们不强制转换enum为<any>类型，那么 TypeScript 将显示错误：

Element implicitly has 'any' type because index expression is not of type 'number'.

元素隐式具有“any”类型，因为索引表达式不是“number”类型。

It means that by default the TypeScript Enum type works with number indexes, i.e. let c = Color[0], but not with string indexes like let c = Color["string"]. This is a known restriction by the Microsoft team for the more general issue Object string indexes.

这意味着默认情况下，TypeScript Enum 类型适用于数字索引，即 let c = Color[0]，但不适用于像let c = Color["string"]. 这是 Microsoft 团队针对更普遍的问题Object string index的已知限制。

回答by Jonas

enum Color{
    Red, Green
}

// To String
 var green: string = Color[Color.Green];

// To Enum / number
var color : Color = Color[green as keyof typeof Color]; //Works with --noImplicitAny

This example works with --noImplicitAnyin TypeScript

此示例适用--noImplicitAny于 TypeScript

Sources:
https://github.com/Microsoft/TypeScript/issues/13775#issuecomment-276381229https://www.typescriptlang.org/docs/handbook/advanced-types.html#index-types

来源：
https: //github.com/Microsoft/TypeScript/issues/13775#issuecomment-276381229 https://www.typescriptlang.org/docs/handbook/advanced-types.html#index-types

回答by Sly_cardinal

This note relates to basarat's answer, not the original question.

此注释与 basarat 的答案有关，而不是原始问题。

I had an odd issue in my own project where the compiler was giving an error roughly equivalent to "cannot convert string to Color" using the equivalent of this code:

我在自己的项目中遇到了一个奇怪的问题，编译器使用以下代码给出了一个大致相当于“无法将字符串转换为颜色”的错误：

var colorId = myOtherObject.colorId; // value "Green";
var color: Color = <Color>Color[colorId]; // TSC error here: Cannot convert string to Color.

I found that the compiler type inferencing was getting confused and it thought that colorIdwas an enum value and not an ID. To fix the problem I had to cast the ID as a string:

我发现编译器类型推断变得混乱，它认为这colorId是一个枚举值而不是一个 ID。为了解决这个问题，我必须将 ID 转换为字符串：

var colorId = <string>myOtherObject.colorId; // Force string value here
var color: Color = Color[colorId]; // Fixes lookup here.

I'm not sure what caused the issue but I'll leave this note here in case anyone runs into the same problem I did.

我不确定是什么导致了这个问题，但我会在这里留下这张便条，以防有人遇到和我一样的问题。

回答by Amitabh

I got it working using the following code.

我使用以下代码让它工作。

var green= "Green";
var color : Color= <Color>Color[green];

回答by alexania

If you provide string values to your enum, a straight cast works just fine.

如果您为枚举提供字符串值，则直接转换就可以了。

enum Color {
  Green = "Green",
  Red = "Red"
}

const color = "Green";
const colorEnum = color as Color;

回答by Nick N.

Given you use typescript: Many of the solutions above might not work or are overly complex.

鉴于您使用打字稿：上述许多解决方案可能不起作用或过于复杂。

Situation: The strings are not the same as the enum values (casing differs)

情况：字符串与枚举值不同（大小写不同）

enum Color {
  Green = "green",
  Red = "red"
}

Just use:

只需使用：

const color = "green" as Color

回答by Chris

I also ran into the same compiler error. Just a slight shorter variation of Sly_cardinal's approach.

我也遇到了同样的编译器错误。只是 Sly_cardinal 方法的一个更短的变体。

var color: Color = Color[<string>colorId];

回答by Luka

If the TypeScript compiler knows that the type of variable is string then this works:

如果 TypeScript 编译器知道变量的类型是字符串，那么这可以工作：

let colorName : string = "Green";
let color : Color = Color[colorName];

Otherwise you should explicitly convert it to a string (to avoid compiler warnings):

否则，您应该将其显式转换为字符串（以避免编译器警告）：

let colorName : any = "Green";
let color : Color = Color["" + colorName];

At runtime both solutions will work.

在运行时，两种解决方案都将起作用。