typescript :是否可以强制 'keyof T' 成为字符串？

Question

我有一个函数类型如下:

const getByPrimaryKey = <E>(list: E[], primaryKey: keyof E): E => {...} 

我可以为与 primaryKey 关联的值添加类型验证吗？例如:

interface User {
  id: string
  name?: string
  age: number
}

const users: User[] = [{id: '1', age: 1}]

getByPrimaryKey<User>(users, 'id') // OK since id is a string
getByPrimaryKey<User>(users, 'name') // NOT OK because name maybe undefined
getByPrimaryKey<User>(users, 'age') // NOT OK because age is a number

Answer 1

您需要结合几个 conditional types .

获取所有非可选键:

type RequiredKeys<T> = { [K in keyof T]-?: ({} extends { [P in K]: T[K] } ? never : K) }[keyof T];

获取具有特定类型值的所有键:

type TypeMatchingKeys<T, V> = { [K in keyof T]: T[K] extends V ? K : never }[keyof T];

然后你可以使用两者的交集:

type NonOptionalTypeMatchingKeys<T, V> = TypeMatchingKeys<T, V> & keyof Pick<T, RequiredKeys<T>>;
const getByPrimaryKey = <E>(list: E[], primaryKey: NonOptionalTypeMatchingKeys<E, string>): E => {
    ...
}