Typescript get function parameter type

Now there's a function update, We want to get its parameter type , What should you do ？ At this time, we need to use Parameters

function updata(state) {
    return {
        router: state.router
    }
}

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Get parameter type ：

type ArrType = Parameters<typeof state>
// ArrType => [state: any]

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If you want to get state The type of ？ You need to use infer

type GetType<T> = T extends (arg: infer P) => void ? P : string;
type StateType = GetType<typeof state>
//  StateType => any
//  because state No type set , therefore ts infer state The type of any

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Translate this code ： (arg: infer P)：arg The type of is to be inferred as P The meaning of the whole code ： If T Can be assigned to (arg: infer P) => void, Then return to P, Otherwise return to string

If you want to get the Return value type , Need to use typescript Built in methods provided ReturnType

type Return = ReturnType<typeof state>
// ReturnType => 
// {
//     router: any;
//}

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