打字稿承诺泛型类型

Question

我有一个示例Promise函数,如下所示.在成功的时候我会回来number并且假的我会回来string.编译器抱怨要为promise指定某种泛型类型.在这种情况下,我要指定什么类型？我要指定喜欢Promise<number>还是Promise<number | string>？

function test(arg: string): Promise {
    return new Promise((resolve, reject) => {
        if (arg === "a") {
            resolve(1);
        } else {
            reject("1");
        }
    });
}

Answer 1

Promise的泛型类型应该对应于函数的非错误返回类型.该错误是隐式的类型any,并未在Promise泛型类型中指定.

例如:

function test(arg: string): Promise<number> {
    return new Promise<number>((resolve, reject) => {
        if (arg === "a") {
            resolve(1);
        } else {
            reject("1");
        }
    });
}

Answer 2

您可以定义一个自定义的 Promise 类型，它实际上也关心拒绝的类型。您也可以只给它一个单一类型，拒绝类型将为any，就像正常的承诺一样。

type CustomPromise<T, F = any> = {
    catch<TResult = never>(
        onrejected?: ((reason: F) => TResult | PromiseLike<TResult>) | undefined | null
    ): Promise<T | TResult>;
} & Promise<T>;

function test(arg: string): CustomPromise<number, string> {
    return new Promise((resolve, reject) => {
        if (arg === "a") {
            resolve(1);
        } else {
            reject("1");
        }
    });
}

const myPromise = test("a");
myPromise.then((value) => {}); //value is of type `number`
myPromise.catch((reason) => {}); //reason is of type `string`