A simple 'OO' closure example

closure_inheritance.js

// Requires node v0.1.100 or a browser with console

function newShape(x, y) {
  return {
    toString: function () {
      return 'Shape at ' + x + ', ' + y;
    }
  };
}

function newCircle(x, y, r) {
  var obj = newShape(x, y);
  var baseToString = obj.toString;
  obj.toString = function () {
    return 'Circular '+ baseToString() + ' with radius ' + r;
  };
  return obj;
}

var shape = newShape(10, 20);
console.log(shape + "");

var circle = newCircle(15, 40, 10);
console.log(circle + "");