example.js

var SquareShape = (function(height){
    var that = {
      area : function () {
         return height * height;
      }
    };
    return that;
});
var RectShape = (function(width, height){
    var that = {
      area : function () {
         return height * width;
      }
    };
    return that;
});

var ComplexShape = (function(shapes) {
   var that = {
      area : function () {
        return shapes.reduce(function(total, curr){
          return total + curr.area();
        }, 0);
      }
    };
    return that;
});

function halvedAreaOf(s) {
    return s.area() / 2;
};

function areaSqrtOf(s) {
    return Math.sqrt(s.area());
};

var square = SquareShape(10);
var rect = RectShape(10, 20);
var complexShape = ComplexShape([square, rect]);

console.log(complexShape.area());
console.log(halvedAreaOf(complexShape));
console.log(areaSqrtOf(complexShape));