Javascript: Function Decorator

decorator.js

// Function Decorator: 

// Takes one function as an argument, returns another function. The returned function is a variation of the argument function. 

function not (fn) { 
  return function (argument) {
    return !fn(argument);
  };
}

function something(x){
  return x !== null;
}

var nothing = not(something);

console.log(something(5));
// true
console.log(nothing(5));
// false