Typescript: Instance of class type

Question

I have the type of a class like here as A_Type?

class A {
  constructor(public a: string) {}
}

type A_Type = {new (a: string): A}

And Id like to get the type of the instance of the A_Type constructor, so that I could type this function explicitly

class A {
  constructor(public a: number) {}
}
//                                              ** not working **
function f<W extends { new(a: number): A }>(e: W): instanceof W {
  return new e(2)
}

let w = f(A)

I am basically searching for the reverse operation of typeof in typescript.

Answer 1

您可以使用内置实用InstanceType<T>程序来执行此操作

class A {
    constructor(public a: number) { }
}

// declare that the return value of the class constructor returns an instance of that class
function f<W extends { new(a: number): InstanceType<W> }>(e: W) {
    return new e(2) // return type is automatically inferred to be InstanceType<W>
}

let w = f(A) // w: A

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