How to automatically apply argument to class constructor?

Question

I have an es6 class User and a global function map() given below:

class  User {
  constructor(public name: string) {}
}

const map = <T, R>(project: (value: T) => R) => {}

Instead of writing the following:

map((value) => new User(value))

I want to (somehow) write something like:

map(new User)

I am not sure if this is possible or not.

Answer 1

You can create a static function in your class that takes the value param and returns a new User:

class User {
  static createUser(value) {
    return new User(value)
  }
}

And then use:

map(User.createUser)

Answer 2

You can't do it directly. If you control the target function (ie it's not the stock map function) you can have it take a constructor instead of the function:

class User { constructor(private id: number) { }}
function map<TIn, T>(value: TIn, ctor: new (a: TIn) => T): T{
    return new ctor(value)
}
map(10, User)

Another more flexible solution is to use a helper function that transform the constructor into the desired function, although it's not much shorter then the original version:

class User { constructor(private id: number) { }}
function ctor<TIn, T>(ctor: new (a: TIn) => T): (value: TIn) => T{
    return value => new ctor(value)
}
[10, 11].map(ctor(User));