努力理解打字稿的减少

Question

假设我将实用程序类型定义为具有所有属性作为字符串的对象

type Stringify<T> = {
  [P in keyof T]: string;
};

，我想定义一个将对象的任何属性转换为字符串的函数，例如

function stringify<T>(obj: T): Stringify<T> {
    return Object.entries(obj).reduce((acc, [k, v]) => {
        acc[k] = `${v}`;
        return acc;
    }, {});
}

我不知道如何定义在 我一直在阅读有关铸造，类型防护和功能过载的每个cicle，

.reduce<Partial<T>>((acc, [k, v]) => /* ... */) // type Partial<T> is not assignable to type Stringify<T>
.reduce((acc: Partial<T>, [k, v]) => /* ... */) // type Partial<T> is not assignable to type Stringify<T>
.reduce(/* ... */, {} as Partial<T>) // type Partial<T> is not assignable to type Stringify<T>

.reduce(/* ...*/
  acc[k] = `${v}`; // Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'Stringify<T>'. No index signature with a parameter of type 'string' was found on type 'Stringify<T>'
}, {} as Stringify<T>)

但我仍然无法为这样一个简单的示例提供解决方案。

Answer 1

您的stringify generic基本上与实用程序类型record进行相同的作业。

您可以使用通用参数充当Record＆lt;字符串，任何＆gt;的速记，以节省一些详细的杂句。

function stringify<T = Record<string, any>>(obj: T): T {
    return Object.entries(obj).reduce((acc, [k, v]) => {
        return { ...acc, [k] : `${v}` }
    }, {} as T);
}

更新：键入返回值作为record＆lt; string，string＆gt;

function stringify<T = Record<string, any>, R = Record<string, string>>(obj: T): R {
    return Object.entries(obj).reduce((acc, [k, v]) => {
        return { ...acc, [k] : `${v}` }
    }, {} as R);
}

const a = stringify({ a: 1, b: 2})

console.log(a)