面试题：TypeScript 高级类型映射类型与运行时数据转换

Question

假设有一个类型`User`定义如下：`type User = {name: string; age: number; email: string;}`，现在你需要创建一个映射类型`PartialUser`，它将`User`类型的所有属性变为可选。然后在运行时，有一个`User`类型的对象，你要将其转换为`PartialUser`类型的对象，同时过滤掉值为`null`或`undefined`的属性。请编写相应的TypeScript代码实现。

Answer 1

type User = {name: string; age: number; email: string;};
type PartialUser = {
    [P in keyof User]?: User[P];
};

function convertToPartialUser(user: User): PartialUser {
    const partialUser: PartialUser = {};
    for (const key in user) {
        if (user.hasOwnProperty(key) && user[key] !== null && user[key]!== undefined) {
            partialUser[key as keyof User] = user[key];
        }
    }
    return partialUser;
}

// 示例使用
const user: User = {name: 'John', age: 30, email: '[e-mail]'};
const partialUser = convertToPartialUser(user);
console.log(partialUser);