nyan.js

var f = function(a){
  return a + 1;
}

var g = function(b){
  return - b
}

function compose(f, g){
  return function(a){
    return g(f(a));
  }
}

console.log( [1, 2, 3, 4].map(compose(f, g)) ); // => [ -2, -3, -4, -5 ]