强制数组在 Typescript 中至少有一个值

Question

是否有一种 Typescript 方法要求数组至少有一个值？例如：

type value = "1" | "2";

export interface ISomething {
  values: value[] // < should be required and have at least one.
}

Answer 1

type value = "1" | "2";

export interface ISomething {
  values: [value, ...value[]] // ← this is the non-empty array type
}

const empty: ISomething = { values: [] }
// Type '[]' is not assignable to type '[value, ...value[]]'.
// Source has 0 element(s) but target requires 1.

const oneValue: ISomething = { values: ["1"] }
// all good :)

您可以选择将其提取以用作通用实用程序类型，如下所示：

export type NonEmptyArray<T> = [T, ...Array<T>];

export interface ISomething {
  values: NonEmptyArray<value>
}

Answer 2

另一种没有接口的方式：

export type NonEmptyArray<Type> = [Type, ...Array<Type>];

用途：

const arrayOfStrings1: NonEmptyArray<string> = ['x']; // valid
const arrayOfStrings2: NonEmptyArray<string> = ['x', 'y']; // valid
const arrayOfStrings3: NonEmptyArray<string> = ['x', 'y', 'z']; // valid
const arrayOfStrings4: NonEmptyArray<string> = [] // invalid
// Type '[]' is not assignable to type '[string, ...string[]]'.
// Source has 0 element(s) but target requires 1.ts(2322)

Answer 3

试试这个

type value = "1" | "2";

export interface ISomething {
  values: {
    0: value,
    [key: number]: value,
  }
}``

Answer 4

您还可以实现一个扩展的接口

Array

:

type value = "1" | "2";

interface IValueArray extends Array<value> {
  0: value; // ensure that at least one 'value' is present
}

export interface ISomething {
  values: IValueArray
}

const something1: ISomething = {
  values: ['1']
}

const something2: ISomething = {
  values: [] // type error
}