如何检查对象是否为TypeScript中的只读数组? [英] How to check if an object is a readonly array in TypeScript?

问题描述

如何使用只读数组(ReadonlyArray)进行数组检查(如Array.isArray())?

How to do an array check (like Array.isArray()) with a readonly array (ReadonlyArray)?

例如:

type ReadonlyArrayTest = ReadonlyArray<string> | string | undefined;

let readonlyArrayTest: ReadonlyArrayTest;

if (readonlyArrayTest && !Array.isArray(readonlyArrayTest)) {
  // Here I expect `readonlyArrayTest` to be a string
  // but the TypeScript compiler thinks it's following:
  // let readonlyArrayTest: string | readonly string[]
}

使用通常的数组，TypeScript编译器可以正确识别它必须是if条件内的字符串.

With an usual array the TypeScript compiler correctly recognises that it must be a string inside the if condition.

推荐答案

与之相关打字稿中出现问题.

@jcalz 提出的建议解决方法正在为isArray的声明添加重载:

Suggested workaround by @jcalz is adding overload to declaration of isArray:

declare global {
    interface ArrayConstructor {
        isArray(arg: ReadonlyArray<any> | any): arg is ReadonlyArray<any>
    }
}

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