Maybe.js

function Nothing() {}
function Just(x) {
  this.valueOf = function(){ return x; };
}

Nothing.prototype.map = function(f) {
  return this;
};
Just.prototype.map = function(f) {
  return new Just(f(this.valueOf()));
};

Nothing.prototype.bind = function(f) {
  return this;
};
Just.prototype.bind = function(f) {
  return f(this.valueOf());
};

var Maybe = {
  fromPossiblyNullValue: function(x) {
    return x == null ? new Nothing() : new Just(x);
  }
};


// double only numbers with odd parity
function doubleOddNumbers(x) {
  // safe version of `return x&1 ? x * 2 : null;`
  return x&1 ? new Just(x * 2) : new Nothing;
}

var a, safeA;

a = null;
safeA = Maybe.fromPossiblyNullValue(a);
safeA.bind(doubleOddNumbers); // Nothing
safeA.bind(doubleOddNumbers).bind(doubleOddNumbers); // Nothing

a = 2;
safeA = Maybe.fromPossiblyNullValue(a);
safeA.bind(doubleOddNumbers); // Nothing
safeA.bind(doubleOddNumbers).bind(doubleOddNumbers); // Nothing

a = 3;
safeA = Maybe.fromPossiblyNullValue(a);
safeA.bind(doubleOddNumbers); // Just(6)
safeA.bind(doubleOddNumbers).bind(doubleOddNumbers); // Nothing