如何根据类方法返回类型声明参数类型

Question

例如：

export const mock = <T>(provide, key: keyof T, value) => (){}
class Service {
do(): boolean {
return true;
}
}
// value have to be Boolean 
mock<Service>(Service, "do", true)

值参数是CCD_ 1函数的返回类型的类型。我想知道是否可以以某种方式声明值的类型。

Answer 1

这是我的解决方案：

/**
* If T is a Class, return union string type of class methods
*/
type ClassType<T> = T extends { new(): infer R } ? keyof R : never
/**
* Check if property is a function/method
*/
type AnyFunc = (...args: any[]) => any
export const mock = <P,>(provide: P, key: ClassType<P>, value: P extends { new(): infer R } ? R[keyof R] extends AnyFunc ? ReturnType<R[keyof R]> : never : never) => {}
class Service {
do(): boolean {
return true;
}
}

const reuslt = mock<typeof Service>(Service, 'do', false) // ok
const reuslt2 = mock<typeof Service>(Service, 'foo', false) // error, expected do
const reuslt3 = mock<typeof Service>(Service, 'do', 42) // error, expected boolean

请记住，TS对待Service型和typeof Service的方式不同。

因为，我不是一个解释大师，这里是你的例子：

const x: Service = {
do: () => true
}
const y: typeof Service = class {
do() {
return true
}
}

TypeScript类文档

更新处理承诺

/**
* If T is a Class, return union string type of class methods
*/
type ClassType<T> = T extends { new(): infer R } ? keyof R : never
/**
* Check if property is a function/method
*/
type AnyFunc = (...args: any[]) => any
type PromiseReturnType<T> = T extends Promise<infer R> ? R : T
export const mock = <P,>(provide: P, key: ClassType<P>, value: P extends { new(): infer R } ? R[keyof R] extends AnyFunc ? PromiseReturnType<ReturnType<R[keyof R]>> : never : never) => { }
class Service {
do() {
return new Promise<number>(resolve => resolve(42))
}
}

const reuslt = mock<typeof Service>(Service, 'do', false) // ok
const reuslt2 = mock<typeof Service>(Service, 'foo', false) // error, expected do
const reuslt3 = mock<typeof Service>(Service, 'do', Promise.resolve(42)) // error, expected number
const reuslt4 = mock<typeof Service>(Service, 'do', 42) // ok