What does the prototype of a user-defined object do?
<pre><code>// Create an object type UserException  
function UserException (message){  
  this.message=message;  
  this.name="UserException";  
}  

// Make the exception convert to a pretty string when used as  
// a string (e.g. by the error console)  
UserException.prototype.toString = function (){  
  return this.name + ': "' + this.message + '"';  
}  
</code></pre>

<p>I don't understand why you need the <code>UserException.prototype</code> here.</p>
