2 ways to write a Functor? (https://github.com/DrBoolean/mostly-adequate-guide/blob/master/ch8.md)

class.js

class Container {
  constructor(x) {
    this.__value = x;
  }

  static of(x) {
    return new Container(x);
  }

  map(f) {
    return Container.of(f(this.__value));
  }
};

export default Container;

function.js

var Container = function (x) {
  this.__value = x;
};

Container.of = function(x) {
  return new Container(x);
};

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

export default Container;