Update Object.prototype.spawn example to use Object.defineProperty no…

…w that node supports it.

articles/prototypal-inheritance/spawn.js

@@ -36,15 +36,15 @@ sys.puts(pete);
 
 
 //proto-spawn
-Object.prototype.spawn = function (props) {
+Object.defineProperty(Object.prototype, "spawn", {value: function (props) {
   var defs = {}, key;
   for (key in props) {
     if (props.hasOwnProperty(key)) {
       defs[key] = {value: props[key], enumerable: true};
     }
   }
   return Object.create(this, defs);
-}
+}});
 
 //animals2
 var Animal = {

articles/prototypical-inheritance.markdown

@@ -51,16 +51,14 @@ Then you can create hierarchies of objects easily:
 
 ## Using `Object.prototype.spawn`
 
-If you're really brave and don't mind messing with `Object.prototype`, then there is an even shorter way:
+Now that node supports `Object.defineProperty`, we can add methods to `Object.prototype` that are not enumerable and thus don't break stuff.
 
 <prototypal-inheritance/spawn.js#proto-spawn*>
 
 Which is used as:
 
 <prototypal-inheritance/spawn.js#animals2*>
 
-Just make sure to understand that adding enumerable properties to Object.prototype breaks all `for ... in` loops that don't have a `hasOwnProperty` check in them.  You've been warned.
-
 ## Where do we go from here?
 
 I'm not sure if this is a good idea or not.  You give up a lot by not having constructor functions that initialize state of objects.  It could be baked into the `Object.spawn` method, but then you're dealing more with classical OOP emulations.