maybe-monad-es2015.js

let compose = (...fns) => x => fns.reverse().reduce((acc, f) => f(acc), x);
let map = f => functor => functor.map(f);

let log = function() {
  console.log(this);
  return this;
};

let Maybe = function(x) {
  this.__value = x;
};

Maybe.of = x => new Maybe(x);

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

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

let safeHead = xs => Maybe.of(xs[0]);
let streetName = compose(map(x => x.street), safeHead);

streetName([])::log();
streetName([{street: 'Shady Ln.', number: 4201}])::log();

maybe-monad-es5.js

'use strict';

var _context;

var compose = function compose() {
  for (var _len = arguments.length, fns = Array(_len), _key = 0; _key < _len; _key++) {
    fns[_key] = arguments[_key];
  }

  return function (x) {
    return fns.reverse().reduce(function (acc, f) {
      return f(acc);
    }, x);
  };
};
var map = function map(f) {
  return function (functor) {
    return functor.map(f);
  };
};

var log = function log() {
  console.log(this);
  return this;
};

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

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

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

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

var safeHead = function safeHead(xs) {
  return Maybe.of(xs[0]);
};
var streetName = compose(map(function (x) {
  return x.street;
}), safeHead);

(_context = streetName([]), log).call(_context);
(_context = streetName([{ street: 'Shady Ln.', number: 4201 }]), log).call(_context);