如何使用类语法复制Javascript构造函数和原型对象

Question

I have a fairly simple example of a Container that stashes a value away and allows you to operate on it in isolation.

For my own interest I've translated the basic structure of this object from .prototype to class syntax. But the example uses a funky method for creating new instances of this object and I can't figure out how to replicate it in class syntax (see code below)

const Container = function(x) {
  this.val = x
}

Container.prototype.map = function(f) {
  return Container.of(f(this.val))
}

Container.of = function(x) { return new Container(x) } // Problem spot

This translates into (class syntax):

class Container {
  constructor(x) {
    this.val = x
  }

  map(f) {
    return Container.of(f(this.val))
  }

  of = (x) => {                       // ????????
    return new Container(x)
  }
}

I believe that the problem is that the "of" method is simply bound to the single original instance of "Container" as a helper to make it easier to not have to write "new" every time you want to spin up an instance of this class. But I can't figure out how to replicate binding like that with the class syntax.

Is it just impossible to instantiate an own-class from one of the classe's own methods?

Answer 1

just declare the function as static .

class Container {
  constructor(x) {
    this.val = x
  }

  map(f) {
    return Container.of(f(this.val))
  }

  static of(x) {                       // ????????
    return new Container(x)
  }
}