反解 promise 类型

umpromisify.ts

type PromiseType<T> = (args: any[]) => Promise<T>;
type UnPromisify<T> = T extends PromiseType<infer U> ? U : never;
// 或者这样一句话： type UnPromisify<T> = T extends (args: any[]) => Promise<infer U> ? U : never;
                                            
// 测试 UnPromisify<T>：
                                                                                        
async function stringPromise() {
  return "string promise";
}
async function numberPromise() {
 return 1;
}


interface Person {
  name: string;
  age: number;
}


async function personPromise() {
  return { name: "Wayou", age: 999 } as Person;
}


type extractStringPromise = UnPromisify<typeof stringPromise>; // string


type extractNumberPromise = UnPromisify<typeof numberPromise>; // number


type extractPersonPromise = UnPromisify<typeof personPromise>; // Person