Adds Object.extend which copies property definitions from one object to another

Object.extend.js

Object.defineProperty(Object, "extend", {
  "configurable": true,
  "enumerable": false,
  "value": function (object, extension) {

    // throw if either is not an object
    if(object !== Object(object)) {throw new TypeError;}
    if(extension !== Object(extension)) {throw new TypeError;}

     // copy property descriptors from extension to object
    Object.getOwnPropertyNames(extension).forEach(function (propertyName) {
      Object.defineProperty(object, propertyName, Object.getOwnPropertyDescriptor(extension, propertyName));
    });

  },
  "writable": true
});