关于 ramda.js：如何将 R.pick 与 TypeScript 一起使用


How to use R.pick with TypeScript

我正在尝试类似

的东西

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import R from 'ramda'
import fs from 'fs'
import path from 'path'
import {promisify} from 'util'

const readFile = promisify(fs.readFile)

export async function discoverPackageInfo(): Promise<{
  name: string,
  version: string
  description: string
}> {
  return readFile(path.join(__dirname, '..', 'package.json'))
    .then(b => b.toString())
    .then(JSON.parse)
    .then(R.pick([
      'name',
      'description',
      'version',
    ]))
}

但我得到了

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src/file.ts:13:3 - error TS2322: Type '{ name: string; version: string; description: string; } | Pick' is not assignable to type '{ name: string; version: string; description: string; }'.
  Type 'Pick' is missing the following properties from type '{ name: string; version: string; description: string; }': name, version, description

 13   return readFile(path.join(__dirname, '..', 'package.json'))
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 14     .then(b => b.toString())
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...
 19       'version',
    ~~~~~~~~~~~~~~~~
 20     ]))
    ~~~~~~~

我做错了什么？

相关讨论

JSON.parse 返回 any。 R.pick 之后的返回类型解析如下：

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.then(R.pick([ 'name', 'description', 'version' ]))
=>
type Return = Pick // resolves to {}; any stems from JSON.parse
type Inner = Exclude<keyof any,
    Exclude<keyof any,"name" |"description" |"version">> // never

你想要 { name: string, version: string description: string }，但得到 {}。要解决此问题，请为 JSON.parse 显式声明所需的类型(我将其命名为 MyThing)：

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readFile(path.join(__dirname,"..","package.json"))
  .then(b => b.toString())
  .then(s => JSON.parse(s) as MyThing)
  .then(R.pick(["name","description","version"]));

可以使解析更加类型安全，例如通过使用断言函数/类型保护：

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export async function discoverPackageInfo(): Promise<MyThing> {
  return readFile(...).then(...)
    .then(safeParse(assertMyThing)) // <-- change
    .then(R.pick(...));
}

const safeParse = < T >(assertFn: (o: any) => asserts o is T) => (s: string) => {
  const parsed = JSON.parse(s);
  assertFn(parsed);
  return parsed;
}

function assertMyThing(o: any): asserts o is MyThing {
  if (!("name" in o) || !("version" in o) || !("description" in o))
    throw Error();
}

Playground(playground 中的外部类型导入可能需要一些时间来加载，否则粘贴到您自己的环境中)

相关讨论