typescript - 打字稿：如何检查一个值是否是有效的枚举键值？

Question

有没有办法在打字稿中获取枚举的名称，比如nameof(FirstEnum)？以下代码有一个丑陋的 if 开关，每次定义新枚举时都必须扩展它。在打字稿中是否有更通用的方法来实现相同的目标？

enum FirstEnum {
    First = 0,
    Second = 1,
    Third = 2,
}
enum SecondEnum {
    One,
    Two,
}


function translateEnum(type$, val): string {
    let lookupKey = '';
    if (type$ === FirstEnum) {
        lookupKey = `firstenum.${FirstEnum[val]}`;
    } else if (type$ === SecondEnum) {
        lookupKey = `secondenum.${SecondEnum[val]}`;
    } else {
        throw new Error('not supported');
    }
    //lookupkey example: secondenum.One
    const result = ''; //translate here, ex. await translationService.translate(lookupkey);
    return result;
}

translateEnum(SecondEnum , SecondEnum.One);

标签： typescript

Answer 1

由于 TypescriptEnums被转换为 JavaScript 对象，因此您可以检查enum键值是否是enumsusingin运算符的成员。请注意，这仅适用于enums不是const基于数字的情况。

enum FirstEnum {
    First = 0,
    Second = 1,
    Third = 2,
}
enum SecondEnum {
    One,
    Two,
}


function translateEnum(val: FirstEnum | SecondEnum): string {
    let lookupKey = '';
    if (val in FirstEnum || val in SecondEnum) {
      console.log(`Enum value ${val} is valid!`);
      //lookupkey example: secondenum.One
      const result = ''; //translate here, ex. await translationService.translate(lookupkey);
      return result;
    } else {
        console.log(`Enum value ${val} not supported.`);
        throw new Error('not supported');
    }
}

translateEnum(SecondEnum.One);

translateEnum(10);

输出

Enum value 0 is valid!
Enum value 10 not supported.
Uncaught Error: not supported
    at translateEnum (eval at <anonymous> (main-0.js:804), <anonymous>:23:15)
    at eval (eval at <anonymous> (main-0.js:804), <anonymous>:27:1)
    at main-0.js:804

更多信息

请参阅堆栈溢出问题Check if value exists in enum in TypeScript。