[英]Object literal may only specify known properties, and 'data' does not exist in type 'PromiseLike<T>'
I have a method that makes a request to a server and, based on the URL, it might return completely differently shaped data.我有一个向服务器发出请求的方法,并且基于 URL,它可能会返回完全不同形状的数据。
Before this I was just casting the expected interface into the returned object:在此之前,我只是将预期的接口转换为返回的 object:
const data = Promise.resolve(makeSignedRequest(requestParameters));
return data as Promise<AwesomeResponse>;
but today I came across this syntax, where I can tell the method explicitly what kind of data I'm expecting:但今天我遇到了这种语法,我可以明确地告诉方法我期待什么样的数据:
const data = Promise.resolve(makeSignedRequest<AwesomeResponse>(requestParameters));
return data;
Now.现在。 the makeSignedRequest may return types like,
AwesomeResponse
, GreatResponse
, AmazingResponse
but there is a common thing in all these. makeSignedRequest 可能会返回诸如
AwesomeResponse
、 GreatResponse
、 AmazingResponse
之类的类型,但所有这些都有一个共同点。 They all share the same structure - the structure of BaseResponse
.它们都共享相同的结构 -
BaseResponse
的结构。
All my responses extend the BaseResponse
, so we're cool there.我所有的回复都扩展了
BaseResponse
,所以我们很酷。
Having said all that, TypeScript is still complaining about the following code:说了这么多,TypeScript 还在抱怨以下代码:
import https from "https";
export interface BaseResponse {
meta: {};
data: Array<{}>;
error?: {
statusCode: number | undefined;
statusMessage: string | undefined;
};
}
export const makeSignedRequest = <T>(url): Promise<T> => {
return new Promise((resolve, reject) => {
// create Request with event listeners
const req = https.request(url, (res) => {
res.on("end", () => {
if (res.statusCode !== 200) {
resolve({
data: [],
meta: {},
error: {}
});
}
});
});
});
};
the resolve({data: [],
gets heavily underlined by VS Code, because as I mentioned in the title, resolve({data: [],
被 VS Code 强调,因为正如我在标题中提到的,
Argument of type '{ data: never[]; meta: {}; error: { statusCode: number | undefined; statusMessage: string | undefined; }; }' is not assignable to parameter of type 'T | PromiseLike<T> | undefined'.
Object literal may only specify known properties, and 'data' does not exist in type 'PromiseLike<T>'.
What am I missing here?我在这里想念什么?
You need a generic constraint :您需要一个通用约束:
export const makeSignedRequest = < T extends BaseResponse > ...
and a type assertion:和类型断言:
resolve({
data: [],
meta: {},
error: {
statusCode: res.statusCode,
statusMessage: res.statusMessage,
},
} as T);
This code works for me in VSCode with TS 3.8.3此代码适用于我在 VSCode 中使用 TS 3.8.3
export interface BaseResponse {
data: [];
meta: {};
error?: {
statusCode: number | undefined;
statusMessage: string | undefined;
};
}
function makeSignedRequest<T extends BaseResponse>(): Promise<T> {
return new Promise((resolve, reject) => {
// create Request with event listener
resolve({
data: [],
meta: {},
error: {},
} as T);
});
}
You are saying that: your function return a generic type Promise, so resolve
only accepts T as parameter.你是说:你的 function 返回一个泛型类型 Promise,所以
resolve
只接受 T 作为参数。 But {data: [], meta: {}, error: {}}
is not T, as T can be anything (string, number...), so it won't compile.但是
{data: [], meta: {}, error: {}}
不是 T,因为 T 可以是任何东西(字符串、数字...),所以它不会编译。 Your function does not make sense with generic type, it should return Promise<BaseReponse>
, that's all.您的 function 对泛型类型没有意义,它应该返回
Promise<BaseReponse>
,仅此而已。 Return Promise<T>
does not produce any benefit Return
Promise<T>
不会产生任何好处
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