使用 const 值作为联合类型选项 Typescript

Question

考虑这个例子：

const FIRST = "FIRST"
const SECOND = "SECOND"

type TOptions = FIRST | SECOND

const someFunction = (options: TOptions): void => {
    // do something, no return
}

我喜欢在类型声明中使用 const 值

type TOptions = FIRST | SECOND // not working

限制选择范围。 这些 const 在整个项目中使用，因此不使用它们并像这样键入它是不明智的：

type TOptions = "FIRST" | "SECOND" // working, as expected

我不想重复自己并且喜欢使用const值作为类型联合选项。

我怎么做？

Answer 1

我相信您需要使用typeof才能使其工作：

const FIRST = 'FIRST'
const SECOND = 'SECOND'

type TOptions = typeof FIRST | typeof SECOND;

const someFunction = (options: TOptions): void => {
// do something, no return
}

someFunction(FIRST); // works
someFunction('test'); // error

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Answer 2

您可以将这些常量声明为类型：

// It's a good idea to export these types 
// since you want them to be used external files
export type FIRST = "FIRST"
export type SECOND = "SECOND"

export type TOptions = FIRST | SECOND

// and then a call to your function will be
someFunction("FIRST") // ok
someFunction("SECOND") // ok
someFunction("THIRD") // Argument of type '"THIRD"' is not assignable to parameter of type 'TOptions'.(2345)

另一种选择是使用枚举类型：

export enum Options {
  FIRST = 'FIRST',
  SECOND = 'SECOND'
}

const otherFunction = (options: Options) => {}

otherFunction(Options.FIRST)
otherFunction(Options.SECOND)