Container

var Container = function(x) {
  this.value = x
}

Functor

var Functor = function(x) {
  this.value = x
}

Functor.prototype.map = function(f) {
  return new Container(f(this.__value)))
}

Maybe

var Maybe = function(x) {
  this.value = x
}

Maybe.prototype.isNothing = function() {
  return (this.__value === null || this.__value === undefined)
}

Maybe.prototype.map = function(f) {
  return this.isNothing() ? new Maybe(null) : new Maybe(f(this.__value))
}