TypeScript:从字符串数组定义联合类型

添加TypeScript 3.4 const assertions 允许将其写成:

const fruits = ["Apple", "Orange", "Pear"] as const;
type Fruits = typeof fruits[number]; // "Apple" | "Orange" | "Pear"

as const TypeScript推断 fruits 以上为 readonly["Apple", "Orange", "Pear"] string[] ,防止 typeof fruits[number]

可以这样做,但首先需要一个额外的函数来帮助推断数组元素的字符串文本类型。默认情况下,Typescript将推断 string[]

function stringLiteralArray<T extends string>(a: T[]) {
    return a;
}

const fruits = stringLiteralArray(["Apple", "Orange", "Pear"]);
type Fruits = typeof fruits[number]

从3.4开始,您还可以使用const类型断言来代替 stringLiteralArray 功能:

const fruits = ["Apple", "Orange", "Pear"] as const;
type Fruits = typeof fruits[number]