检查 Enum 中是否存在字符串

Question

这不是 Check if value exists in enum in TypeScript 的副本，它根据 Enum 值检查类型 Enum。

没有其他关于 TypeScript 如何根据枚举检查字符串或字符串文字的帖子。原因是我通过 API 接收数据，所以它的原始类型是字符串。

代码：

enum Method {
    Get = 'get',
    Put = 'put',
    Post = 'post',
    Patch = 'patch',
    Delete = 'delete'
}

console.log(Method);
console.log('get' in Method);
console.log(Object.values(Method));
console.log(Object.values(Method).includes('get'));

输出：

src/libs/async-express/test.ts:12:44 - error TS2345: Argument of type '"get"' is not assignable to parameter of type 'Method'.

12 console.log(Object.values(Method).includes('get'));

在 Java 中会这样：

public static boolean contains(String test) {
    for (Choice c : Choice.values()) {
        if (c.name().equals(test)) {
            return true;
        }
    }
    return false;
}

在 TypeScript 中执行此操作的任何标准方法。

Answer 1

刚刚意识到你可以投射：

Object.values(Method).includes(type as Method);

Answer 2

为避免强制类型转换，您可以在Object.values- 中添加类型注释 这只是从Method[] 扩大了它。

但是如果你需要成功地缩小类型，你应该使用类型保护；否则您将无法将变量传递给仅接受Method 的其他函数。

// type guard fn
const isMethod = (maybeMethod: string): maybeMethod is Method => {
  // explicityly type the values of Method as an array of strings,
  // so they can be compared to possible invalid methods
  const validMethods: string[] = Object.values(Method);
  return validMethods.includes(maybeMethod);
};

// fn to demonstrate narrowing behavior
const foo = (maybeMethod: string) => {
  if (isMethod(maybeMethod)) {
    // compiler successfully narrows the type, and
    const clone = maybeMethod; // (parameter) maybeMethod: Method
  }

  if (Object.values(Method).includes(maybeMethod as Method)) {
    // the type has not actually been narrowed.
    // maybeMethod is still just a string.
    const clone = maybeMethod; // (parameter) maybeMethod: string
  }
};

Answer 3

最简单的方法（正如您自己注意到的）是使用强制转换。

// Implicit cast
const allMethods: string[] = Object.values(Method);
console.log(allMethods.includes("get"));

// Explicit cast
console.log((Object.values(Method) as string[]).includes("get"));