Typescript Record<number, string> 接受 Key 上的数字

Question

我是 typescript 的新手，还有很多东西要学习，但我偶然发现了这个 code，这让我对 Record 实用程序类型感到非常困惑。

此代码适用于 playground

const data = async (name: string, id: number): Promise<Record<number,string>> => {
  const obj = {
    foo: 'bar', //shouldn't this not work since I've used 'number'?
  }
  return obj
}

这个没有（第2行）

const foo1: Record<string, string> = { foo: 'bar' }
const foo2: Record<number, string> = { foo: 'bar' }

这是为什么？我也不确定 'key' 中应该使用哪种数据类型。尝试打字稿游乐场

Answer 1

这是因为TS要兼容JavaScript.

考虑这个纯 js 代码：

const foo={
  0:42
}

const x = foo['0'] // number
const y = foo[0] // number

您可能已经注意到，JS 允许您同时使用字符串和数字键 0: 42

同时查看 js 和 ts 文档：

js explanation

Property names Property names are string or Symbol. Any other value, including a number, is coerced to a string. This outputs 'value', since 1 is coerced into '1'.

ts explanation

It is possible to support both types of indexers, but the type returned from a numeric indexer must be a subtype of the type returned from the string indexer. This is because when indexing with a number, JavaScript will actually convert that to a string before indexing into an object. That means that indexing with 100 (a number) is the same thing as indexing with "100" (a string), so the two need to be consistent.

这是为什么呢？我也不确定 'key'.

中应该使用哪种数据类型

TypeScript 已为键内置类型：type PropertyKey = string | number | symbol

您可以在不声明的情况下使用 PropertyKey。此类型内置

Typescript Record<number, string> 接受 Key 上的数字

Typescript Record<number, string> accepts number on Key

promise

typescript