动态访问的对象属性的Typescript类型推断

Question

interface CustomResponse {
    data: string;
    status: number;
    [key: string]: string | number;
}

const RESPONSE_PROPS = {
  DATA: "data",
  STATUS: "status",
};

const response: CustomResponse = {
    data: "test",
    status: 200,
};

let dataWrong: string = response[RESPONSE_PROPS.DATA];
let dataRight: string = response.data;

dataWrong获取错误

Type 'string | number' is not assignable to type 'string'. Type 'number' is not assignable to type 'string'

在上面这样的情况下，如何获取dataWrong在打字稿中推断出正确的类型？ 类型断言（更好的类型守卫）是唯一的方法吗？

Answer 1

如果使用as const断言（这将使编译器保持RESPONSE_PROPS.DATA的字符串文字类型为"data" ），则RESPONSE_PROPS.DATA将键入为string它按预期工作：

interface CustomResponse {
    data: string;
    status: number;
    // [key: string]: string | number; not necessary for the code to work
}

const RESPONSE_PROPS = {
    DATA: "data",
    STATUS: "status",
} as const;

const response: CustomResponse = {
    data: "test",
    status: 200,
};

let dataWrong: string = response[RESPONSE_PROPS.DATA];
let dataRight: string = response.data;

注意：如果字符串文字类型用于索引，则不需要索引签名。