monads.js

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

// Functor's `fmap` in Haskell
Container.prototype.map = function(f) {
  return new Container(f(this.val));
};

// Monad's `>>=` (pronounced bind) in Haskell
Container.prototype.flatMap = function(f) {
  return f(this.val);
};

// Monad's `return` in Haskell
Container.of = function(val) {
  return new Container(val);
};

var c = Container.of(2);

c.map(function(x) {
  return x+2;
}); // === Container.of(4)

c.flatMap(function(x){
  return Container.of(x+2);
}).flatMap(function(x){
  return Container.of(x * -1);
}); // === Container.of(-4)

Yep! https://gist.github.com/pselle/fd156a219c56aab529f3#comment-1318385