如何将字符串转换为 Typescript 中的枚举 [英] How can I cast a string to an enum in Typescript

问题描述

枚举定义:

enum Colors {
  Red = "red",
  Blue = "blue"
}

如何将一些任意的字符串(例如来自 GET 请求的结果)投射到枚举中?

How can I cast some arbitrary sting (e.g. a result from a GET request) to the enum?

const color: Colors = "blue"; // Gives an error

我知道在这里可以使用联合，但是我需要使用一个库，并且在这个库中他们使用的是枚举.所以我必须将我的字符串转换为它们的枚举类型.

I understand that a union can be used here instead, but there is a library that I need to use and in this library they are using an enum. So I have to cast my string into their enum type.

此外，为什么整数枚举可以工作，而字符串枚举却没有相同的行为?

In addition, why do integer enums work but string enums fail to have the same behavior?

enum Colors {
  Red = 1,
  Blue
}

const color: Colors = 1; // Works

推荐答案

如果您确定字符串将始终对应于枚举中的一个项目，那么将其强制转换应该没问题:

If you are sure that the strings will always correspond to an item in the enum, it should be alright to cast it:

enum Colors {
  Red = "red",
  Blue = "blue",
}

const color: Colors = <Colors> "blue";

它不会捕获字符串无效的情况.您必须在运行时进行检查:

It won't catch the cases where the string is not valid. You would have to do the check at runtime:

let colorName: string = "blue"; // from somewhere else
let color: Colors;
if (Object.values(Colors).some((col: string) => col === colorName))
  color = <Colors> colorName;
else
  // throw Exception or set default...

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