Typescript 使用字符串文字数组作为类型

我想使用单个数组

constfruits=['banana'、'apple'、'orange']

作为普通数组和

类型

我应该能够做到这一点：
const x:fruits/=>只接受“香蕉”、“苹果”或“橙色”

并且能够做到这一点：
@IsIn（水果）


我已尝试将数组声明为
，例如：

const fruits=['香蕉'、'苹果'、'橘子']
type Fruits=typeof Fruits[number]//计算结果为类型：“香蕉”|“苹果”|“橙色”

但是
@IsIn（水果）
将返回以下错误：

Argument of type 'readonly ["banana", "apple", "orange"]' is not assignable to parameter of type 'any[]'.
  The type 'readonly ["banana", "apple", "orange"]' is 'readonly' and cannot be assigned to the mutable type 'any[]'.ts(2345)

所以我想如果我创建了两个数组，一个普通数组和一个只读数组，它应该可以工作。所以我试了一下：

const fruits=['香蕉'、'苹果'、'橘子']
const FROUTS_readonly:[…FROUTS]
水果类型=水果类型\u只读[数量]

但是现在
Fruits
evalute到
type:string
而不是
type:“banana”|“apple”|“orange”
的确，使用
readonly
元素生成对象和数组。如果您想获得
const
断言为您带来的字符串文字和元组类型的好处，同时还可以取消对结果的只读操作，那么您可以编写一个帮助函数来实现这一点。我将其称为
mutable（）
：

对上述情况也是如此

const alsoFruits = deepMutable(['banana', 'apple', 'orange'] as const);
// const alsoFruits: ["banana", "apple", "orange"]

但对于嵌套对象，这种区别变得很重要：

const readonlyDeepFruits = {
    yellow: ["banana", "lemon"],
    red: ["cherry", "apple"],
    orange: ["orange", "mango"],
    green: ["lime", "watermelon"]
} as const;
/* const readonlyDeepFruits: {
    readonly yellow: readonly ["banana", "lemon"];
    readonly red: readonly ["cherry", "apple"];
    readonly orange: readonly ["orange", "mango"];
    readonly green: readonly ["lime", "watermelon"];
} */

const partiallyMutableDeepFruits = mutable(readonlyDeepFruits);
/* const partiallyMutableDeepFruits: {
    yellow: readonly ["banana", "lemon"];
    red: readonly ["cherry", "apple"];
    orange: readonly ["orange", "mango"];
    green: readonly ["lime", "watermelon"];
} */

const fullyMutableDeepFruits = deepMutable(readonlyDeepFruits);
/* const fullyMutableDeepFruits: {
    yellow: ["banana", "lemon"];
    red: ["cherry", "apple"];
    orange: ["orange", "mango"];
    green: ["lime", "watermelon"];
} */

好的，希望能有帮助。祝你好运

谢谢，这有用：）但我还是不明白为什么
typeof fruits\u readonly[number]
的计算结果不是
type:“香蕉”|“苹果”|“橙色”
。请你给我解释一下好吗？哦，对不起。。。在
const fruits=['banana'、'apple'、'orange']
中，
fruits
被推断为类型
string[]
，因此编译器已经忘记了传递给它的特定字符串的标识。所以
[…水果]
也将是
字符串[]
。如果你想让编译器记住
“香蕉”|“苹果”|“橙色”
，你需要告诉它不要在信息还在的时候扔掉信息。。。这就是const所做的（除其他外）。
const alsoFruits = deepMutable(['banana', 'apple', 'orange'] as const);
// const alsoFruits: ["banana", "apple", "orange"]

const readonlyDeepFruits = {
    yellow: ["banana", "lemon"],
    red: ["cherry", "apple"],
    orange: ["orange", "mango"],
    green: ["lime", "watermelon"]
} as const;
/* const readonlyDeepFruits: {
    readonly yellow: readonly ["banana", "lemon"];
    readonly red: readonly ["cherry", "apple"];
    readonly orange: readonly ["orange", "mango"];
    readonly green: readonly ["lime", "watermelon"];
} */

const partiallyMutableDeepFruits = mutable(readonlyDeepFruits);
/* const partiallyMutableDeepFruits: {
    yellow: readonly ["banana", "lemon"];
    red: readonly ["cherry", "apple"];
    orange: readonly ["orange", "mango"];
    green: readonly ["lime", "watermelon"];
} */

const fullyMutableDeepFruits = deepMutable(readonlyDeepFruits);
/* const fullyMutableDeepFruits: {
    yellow: ["banana", "lemon"];
    red: ["cherry", "apple"];
    orange: ["orange", "mango"];
    green: ["lime", "watermelon"];
} */