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typescript - 如何检查给定值是否在联合类型数组中

问题描述

我有一个给定联合类型的数组，然后想检查来自联合类型超集的字符串是否包含在数组中（运行时检查）：

const validOptions: ("foo" | "bar")[] = ["foo", "bar"]
type IArrType = typeof validOptions[number]
const key: IArrType | "alien" = "alien" // Rather: some random function
const isKeyInArr = validOptions.indexOf(key) > -1 // Error: "alien" is not assignable to "foo" | "bar"

// Fix 1:
const isKeyValidCast = validOptions.indexOf(<IArrType>key) > -1 
// Fix 2:
const isKeyValidExplicit = 
      key === "alien" ? false : validOptions.indexOf(key) > -1 // OK: type guard magic

修复 1 可以，但不是很优雅。Fix 2 欺骗了编译器，但运行时具有误导性和低效。在我的情况下，“外星人”字符串类型只是任何不在联合类型中的字符串的占位符。

有没有什么方法可以在没有强制转换或显式测试的情况下编译？可以否定表达式，以便我们让这个“类型保护”工作吗？

顺便说一句：这个非常酷的答案展示了如何从值列表构造类型化元组：Typescript 从元组/数组值中派生联合类型

标签： typescript

解决方案

The accepted answer uses type assertions/casting but from the comments it appears the OP went with a solution using find that works differently. I prefer that solution also, so here's how that can work:

const configKeys = ['foo', 'bar'] as const;
type ConfigKey = typeof configKeys[number]; // "foo" | "bar"

// Return a typed ConfigKey from a string read at runtime (or throw if invalid).
function getTypedConfigKey(maybeConfigKey: string): ConfigKey {
    const configKey = configKeys.find((validKey) => validKey === maybeConfigKey);
    if (configKey) {
        return configKey;
    }
    throw new Error(`String "${maybeConfigKey}" is not a valid config key.`);
}

Note that this can guarantee that a string is a valid ConfigKey both at runtime and compile time.

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