typescript 在打字稿中，如何定义异步函数的类型
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In typescript, how to define type of async function
提问by Ron
I tried to define a type of async function, but failed in compilation, see below:
我试图定义一种异步函数，但编译失败，见下文：
interface SearchFn {
async (subString: string): string;
}
class A {
private Fn: SearchFn
public async do():Promise<string> {
await this.Fn("fds") // complain here: cannot invoke an expression whose type lacks a call signature
return ''
}
}
Can anyone help me work this out?
谁能帮我解决这个问题？
回答by Thiago Barcala
Found this searching how to declare a "typedef" for an async arrow function.
发现这个搜索如何为异步箭头函数声明“typedef”。
It works if you just declare the return type of the function to be a Promise:
如果你只是将函数的返回类型声明为一个 Promise，它就可以工作：
interface SearchFn {
(subString: string): Promise<boolean>;
}
or as a type declaration:
或作为类型声明：
type SearchFn = (subString: string) => Promise<boolean>;
Microsoft's TS Linter will recommend this second syntax.
Microsoft 的 TS Linter 将推荐第二种语法。
回答by Motti
The asynckeyword is used to indicate to the compiler/runtime that the function in question will use awaitinternally (so it can put in the required scaffolding to enable it).
该async关键字用于向编译器/运行时指示相关函数将在await内部使用（因此它可以放入所需的脚手架以启用它）。
This means that asynconly has meaning for the implementationof the function, not it's interface. Therefore having asyncon an interface's method isn't useful, you want to say that the function returns a certain Promise(in your case Promise<string>) but you don't want to enforce that the interface's implementer implements this in a certain way (using await).
这意味着async它只对函数的实现有意义，而不是它的interface。因此，async拥有接口的方法没有用，您想说该函数返回某个Promise（在您的情况下Promise<string>），但您不想强制接口的实现者以某种方式（使用await）实现它。
So as other said before me:
所以正如其他人在我之前所说：
interface SearchFn {
(subString: string): Promise<string>;
}
Then whoever chooses to implement this function can choose to use async, plain old Promise.thenor perhaps even some new methodology that will come up in the future.
然后，选择实现此功能的任何人都可以选择使用async，简单的旧方法Promise.then或什至将来会出现的一些新方法。
回答by Ben Carp
Pass the type of the returned object to the Promise generic.
将返回对象的类型传递给 Promise 泛型。
type SearchFn = (subString: string): Promise<string>;
Alternatively you can declare an AsyncFunctiongeneric type.
或者，您可以声明一个AsyncFunction泛型类型。
type AsyncFunction <A,O> = (...args:A) => Promise<O>
type SearchFn = AsyncFunction<[string], string>
AsyncFunction is a type generic that receives two type variables - the type of the input(A), and the type of the output.
AsyncFunction 是一个类型泛型，它接收两个类型变量——输入（A）的类型和输出的类型。
回答by Jeff Gu Kang
Simple Way.
简单的方法。
export interface SignUpReturn {
user_id: string
platform: string
name: string
image_url: string
email: string
}
export interface SignUpType {
platform: string
loginId: string
password: string
name: string
email: string
}
const SignUp = async (userInfo: SignUpType) => {
try {
const data: SignUpReturn = await client.request(query, userInfo)
return data
} catch (error) {
throw error
}
}
export default SignUp
or
或者
const SignUp = async (userInfo: SignUpType): Promise<SignUpReturn> => {
try {
const data = await client.request(query, userInfo)
return data
} catch (error) {
throw error
}
}
