Typescript 在返回嵌套对象时不返回嵌套类型

Question

我希望我的函数返回嵌套类型的内容，但即使我们确定应该返回的类型，它也不起作用。让我们看一个例子:

type Content = {
    some: {
        extra: string;
        prop: number;
    },
    other: string,
    somenumber: number
}

const factory = (content: Content) => {
    return (key: keyof Content) => {
        return content[key];
    };
};

const content:Content = {
    some: {
        extra: "wow",
        prop: 123
    },
    other: "abc",
    somenumber: 999
};

const el = factory(content);
const some = el("some"); // good, I can pass only existing key as a string
console.log(some.extra); // error, can't reach "extra"

LIVE EXAMPLE

我希望“some”包含并提出“extra”和“prop”，但采用“extra”会抛出 TypeScript。

Answer 1

使用泛型类型参数定义您的函数，以便 Typescript 可以正确推断类型:

const factory = (content: Content) => {
    return <K extends keyof Content>(key: K) => {
        return content[key];
    };
};

See this live example.