Inspecting object in javascript

An interesting problem is to inspect unknown objects in javascript. Found a good example of how to do it here. Just to rehash in case the site move:

function inspect(obj, maxLevels, level)
{
 var str = '', type, msg;

   // Start Input Validations
   // Don't touch, we start iterating at level zero
   if(level == null)  level = 0;

   // At least you want to show the first level
   if(maxLevels == null) maxLevels = 1;
   if(maxLevels < 1)    
       return '<font color="red">Error: Levels number must be > 0</font>';

   // We start with a non null object
   if(obj == null)
   return '<font color="red">Error: Object <b>NULL</b></font>';
   // End Input Validations

   // Each Iteration must be indented
   str += '<ul>';

   // Start iterations for all objects in obj
   for(property in obj)
   {
     try
     {
         // Show "property" and "type property"
         type =  typeof(obj[property]);
         str += '<li>(' + type + ') ' + property +
                ( (obj[property]==null)?(': <b>null</b>'):('')) + '</li>';

         // We keep iterating if this property is an Object, non null
         // and we are inside the required number of levels
         if((type == 'object') && (obj[property] != null) && (level+1 < maxLevels))
         str += inspect(obj[property], maxLevels, level+1);
     }
     catch(err)
     {
       // Is there some properties in obj we can't access? Print it red.
       if(typeof(err) == 'string') msg = err;
       else if(err.message)        msg = err.message;
       else if(err.description)    msg = err.description;
       else                        msg = 'Unknown';

       str += '<li><font color="red">(Error) ' + property + ': ' + msg +'</font></li>';
     }
   }

     // Close indent
     str += '</ul>';

   return str;
}